# Battery Sizing - am I crazy?



## chartscharts (Aug 1, 2006)

All,

My CAL29 is in need of new batteries. The existing ones are shot and won't hold a charge. I wanted to solicit opinions about downsizing drastically.

My existing batteries are a bank of two of these: Trojan EV8D, 12Volt, [email protected], batteries. They are big and weigh a gazillion pounds a piece. More than I can easily remove myself, a big disadvantage.

My needs are modest. It primarily needs to start my Farymann A30, single cylinder, 10HP diesel. I have the usual running lights and house lights and VHF radio.

My sailing habits are almost exclusively day sailing. 2-3 times a year (on good years) I'll take it out for an overnight. I could use battery powered camping lanterns on those even, since it's not very often.

So I think I might be able to drastically downsize, allowing for easier and cheaper maintenance and replacement. Going to something like two of these:

EverStart Group Size 29DC Marine Battery: Automotive : Walmart.com

Am I crazy? What am I not thinking of?

-Charts


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## Minnewaska (Feb 21, 2010)

Those are big dogs at 155 lbs a piece. No shame in not wanting to haul those in and out. 

If you can size a smaller battery at 2x your normal usage, then go for it. You could always replace the 8D with two smaller batts that are connected in parallel.


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## blt2ski (May 5, 2005)

You need to do something like I have in my 30' boat. I have a typical size 24 starting battery for my 2 cy Yanmar, then a separate house battery that is a true deep cycle battery. They should not be run together for house lighting etc needs. You might find depending upon useage, a size 24, 27 or 31 12V lead DCycle batter will work for your needs. If you are going say a week at a time, then yes, keep the 2 8D's if that is what you have. Reality is, my setup will work for what you have. I did have a size 24 for the house, recently put in a 31 for a few more AHrs to work with. 

Marty


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## asdf38 (Jul 7, 2010)

It's hard to argue with simplicity. It looks like you chose a deep cycle which in my opinion would be the best thing to do if you're going with one battery. Deep cycles still have plenty of cranking power and you're one cylinder isn't going to draw a ton.

However I don't know that particular battery and the usual battery purchasing cautions apply: if you want a deep cycle, make sure it's really a deep cycle. Deep cycles will always have the 20 hour Ah rate marked on them. That said I know plenty of people around here go with Wal-Mart. If you have a Sam's Club nearby also consider this:
http://www.sailnet.com/forums/electrical-systems/77173-battery-buyers-good-news.html

But also consider that you'll have no reserve bank should you leave a cabin light on and drain your one battery. Then you'll be stuck. One thing I considered with my 1 cylinder Yanmar was using a small $35 tractor battery as a reserve/start instead of a standard marine size one. You could consider that too if you wanted the usual reserve bank functionality but without much cost or weight.
http://www.samsclub.com/sams/durace...-size-eu1l/prod3590226.ip?navAction=push#spec


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## Waltthesalt (Sep 22, 2009)

I agree with what's been said and your plan. If you're not going to do any rewiring then you want both the batteries to be the same type and age so that you charge them in parallel. It appears that someone wanted to have the battery bank be a larger capacity than needed for engine starting and light loading. The current, and more practical, thought to address this is to have a bigger deep cycle type battery for the hotel loads and a smaller starting battery that's spec'd to your engine requirements. with this type of arrangement however you'll need a different battery distribution panel which one battery is for the engine and the other for hotel loads, with a cross connect feature. You'll also need a charging circuit that uses a VSR relay or duo type charge that allows for the fact that the different batteries charge at differrent times and rates.


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## chucklesR (Sep 17, 2007)

Somebody sold the previous owner a massive bank or batteries, or his usage was much different that yours.

Your plan is fine for your intended usage. Good luck getting the old ones out, use the boom as a lifting arm  and wear something you don't like, or a plastic suit over it.


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## Siamese (May 9, 2007)

I would not use the battery that you linked to at Walmart. Not sure if it's a true deep cycle, and I would DEFINITELY not buy a maintenance free battery for a boat. 

Get a deep cycle 12v battery, that you can maintain. Without going into the mechanics of how they achieve "maintenance free" status, I will keep this brief and tell you it's not what you want. 

I would typically suggest a bank of two 6v golf cart batteries and a 12v starting battery for emergencies, but for the needs you stated, a conventional lead acid deep cycle battery will serve you well. Keep some distilled water on board and top off the battery regularly.


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## MedSailor (Mar 30, 2008)

chartscharts said:


> My sailing habits are almost exclusively day sailing. 2-3 times a year (on good years) I'll take it out for an overnight.
> -Charts


Ummm.... I don't think you have too much battery capacity, I think you're just not sailing enough! Sail more and stay out longer and then you'll need the batteries! 

Drastically downsizing your bank sounds like a very good idea. Just make sure to have 2 separate batteries: one starter style and one deep cycle. I think just about any size and brand would work from group 24 up based on your modest needs.

MedSailor


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## hellosailor (Apr 11, 2006)

440AH of batteries for mostly daytripping?

You're not crazy. Get two 29D's, leave the battery switch on 'both' most of the time. When you drop the hook and there's a chance you might dawdle and run a battery down, then split the batteries, so you know you'll have one left for starting. No big deal and simplicity pretty much trumps all the theories and options.

In fact, for your use? One 29D or one 31 would probably suffice. Add a "battery brain" or other low-voltage cut-out on the positive post, and that will cut off all loads when you reach a low voltage, saving just enough battery so you can start the engine back up again. No master switch required, just reset it if you pull the battery down that low.


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## Barquito (Dec 5, 2007)

I'm guessing you can exchange those huge batteries for a little cabbage($$).


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## MarkofSeaLife (Nov 7, 2010)

chartscharts said:


> My sailing habits are almost exclusively day sailing. 2-3 times a year (on good years) I'll take it out for an overnight. I could use battery powered camping lanterns on those even, since it's not very often.
> 
> -Charts


I dont think you need a deep cycle battery at all.

I dont think you need 2 batteries.

I think you need one quite small battery, like a 55 amp hour one. I dont know what they call them in the USA. But one small, good battery. Walmart or some other large auto store brand battery should be fine.

I just looked up a thing and it said Group 29 is 115 amp hours. I really dont think you need anything like that whatsoever. I suggest HALF that size.

For your overnight trips , as you say, take a camping lantern etc. If you sail overnight and the battery gets low just bung on the engine for a bit and charge it


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## asdf38 (Jul 7, 2010)

MarkofSeaLife said:


> I dont think you need 2 batteries.


You definitely want a deep cycle. Deep cycles can start all day long with no harm. Starting batteries however have limited capacity and very bad lifetime if they are ever deep cycled.

Even a small Group 24 deep cycle can start that 1 cylinder engine with ease and will then have far more capacity for running the radio/lights after that.


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## SloopJonB (Jun 6, 2011)

Unless you have the option of hand starting your engine, I'd go with two automobile size deep cycles on a selector switch. Alternate them for starting the engine and switch to one only for house use - then if it dies you'll still be able to start your engine in the morning.

Switching to LED lighting will help a ton as well.

I know Deep Cycle batteries are not supposed to be starting batteries but I've used them that way and got nine years out of one $75 one with no problems.


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## chef2sail (Nov 27, 2007)

Better not to short yourself and not have enough power should you want to add things on the future

I would go with 4 golf cart batteries deep cycle. These way about 45 lbs each and are easily manuevered by one person. 2 of these is about the same footprint of a group 31. Four would be the same size almost as 1 of you 8Ds with the same amp hours of 2 8ds

4- 6 volt golf carts =440 ah = 220 usable ah. Refrigeration should you ever add it will run between 50-75 ah a day.

Better to have to much than to little IMHO.

Dave


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## asdf38 (Jul 7, 2010)

SloopJonB said:


> I know Deep Cycle batteries are not supposed to be starting batteries but I've used them that way and got nine years out of one $75 one with no problems.


Not true...

Starting used as deep cycle = BAD
Deep cycle used as starting = No prob

Essentially the ONLY advantage to starting batteries is that they have more cranking camps for a particular size/weight. Given the deep cycle need for a usual boat versus it's engine size however there is usually no need for the extra CCA's.

From another thread:


Main Sail said:


> Trojan Battery does an excellent job:
> 
> "Q: Can I use my Deep Cycle battery as a starting battery?
> 
> A: Deep cycle batteries can be used for engine starting but starting batteries should not be used for deep cycle applications. A deep cycle battery may have less cranking amps per pound than a starting battery, but in most cases a deep cycle battery is still more than adequate for the purpose of starting an engine."


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## MarkofSeaLife (Nov 7, 2010)

Yes, but read the ops post

He is NOT going to deep cycle the batteries.
He is only using them to start. He's taking a camping light. No refrigeration.
Where, tell me is there deep cycle in his elec usage?

There's not.

Read his post.


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## asdf38 (Jul 7, 2010)

MarkofSeaLife said:


> Yes, but read the ops post
> 
> He is NOT going to deep cycle the batteries.
> He is NLT sing them to start. He's taking a camping light. No refrigeration.
> ...


And the flip side of that question is what advantage does the starting battery have?

If it has 6x the CCA requirement of the engine the answer is very little. Meanwhile those extra unused CCA's come at the expense of Ah's that can actually be used for lights and the radio. On top of that the design compromises that squeeze out the extra cranking amps severely reduce the lifetime of the battery when it's deep cycled.

Starting batteries are essentially tailored for cars which 1) Have giant engines for their size which need lots of CCA's and 2) run the engine 99% of the time they're used.

By contrast, sailboats go days between charges and have lights and radios which over a couple days of cruising can easily use up 20-40% of a smallish bank (especially if they're not LED). I just have a hard time seeing a use-case constructed where the starting battery is a better choice.


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## blt2ski (May 5, 2005)

MarkofSeaLife said:


> Yes, but read the ops post
> 
> He is NOT going to deep cycle the batteries.
> He is only using them to start. He's taking a camping light. No refrigeration.
> ...


Actually, I did reread after this post, YOU need to reread the post, This sentence does stand out as not only needing to start the motor, but run on occasion the running and house lights, along with CB radio!

"My needs are modest. It primarily needs to start my Farymann A30, single cylinder, 10HP diesel. I have the usual running lights and house lights and VHF radio."

Reality is, he "could" get away with a single dual purpose battery, or two dual or Deepcycle batteries, or a single ea starting and house battery! The best option no matter how one slices it, is two batteries, not a single one. If the house, running lights, CB etc drain the batter too low, he will not start his engine! Hence why most of us will recommend 2 separate use batteries.

Now if one wants to argue about the size of ea, I'm not going there! as that has too many variables that come into play! Some would say his current 2 8D bats are too little! others a single size 24 75ahr battery is plenty for a house bank!

marty


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## JimsCAL (May 23, 2007)

I survived with no problem with two Group 27 deep cycles on my previous 30 footer with a 2-cylinder Universal diesel. Even on 2+ week cruises. Current boat has two Group 31 deep cycles and also fine with similar usage. They start my Yanmar 3GM with no problem. You could go with one starting and one deep cycle, but I would just go with two the same to keep things simple.


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## CaptTom (Aug 27, 2012)

Siamese said:


> I would typically suggest a bank of two 6v golf cart batteries and a 12v starting battery for emergencies, but for the needs you stated, a conventional lead acid deep cycle battery will serve you well. Keep some distilled water on board and top off the battery regularly.


Agreed. The advantages to the 6V GC batteries are high AH rating for their size and cost, full deep-cycle capability, a smaller footprint that gives you some mounting flexibility, and an easier job installing and removing them. Sam's club also sells GC batteries, as does Batteries Plus.

I agree you would do fine with a conventional 12V battery, but at least spec out a pair of GC batteries, you may find that works better for you.


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## asdf38 (Jul 7, 2010)

CaptTom said:


> Agreed. The advantages to the 6V GC batteries are high AH rating for their size and cost, full deep-cycle capability, a smaller footprint that gives you some mounting flexibility, and an easier job installing and removing them. Sam's club also sells GC batteries, as does Batteries Plus.
> 
> I agree you would do fine with a conventional 12V battery, but at least spec out a pair of GC batteries, you may find that works better for you.


They do have lots of Ah's but of course it takes two before you can compare those Ah's to a 12V battery. In terms of energy density by weight you can compare two 60lb batteries on Deka's website:

21.35 Wh/lb for the Group 31 (59 lbs, 105ah)
21.32 Wh/lb for the Golf Cart GC10 (60.5 lbs, 215ah)

Basically a rounding error in terms of the difference. I've run the numbers on density by volume and again it comes out the same. So there may be advantages for the GC's but it's not density.

http://www.dekabatteries.com/assets/base/0248ProMasterGolf.pdf
http://www.dekabatteries.com/assets/base/0194.pdf


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## chef2sail (Nov 27, 2007)

> They do have lots of Ah's but of course it takes two before you can compare those Ah's to a 12V battery. In terms of energy density by weight you can compare two 60lb batteries on Deka's website:
> 
> 21.35 Wh/lb for the Group 31 (59 lbs, 105ah)
> 21.32 Wh/lb for the Golf Cart GC10 (60.5 lbs, 215ah)
> ...


Not sure what this means.

Of course you need two 6- volts to get 12 volt current. The advantage of them is that the footprint for the 2- 6 volt is almost the same as 1 12 volt. So for the same footprint you get twice the ah. NOt sure what density has to do with it. The advantage is more for the SIZE...irrespective of weight.


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## asdf38 (Jul 7, 2010)

chef2sail said:


> Not sure what this means.
> 
> Of course you need two 6- volts to get 12 volt current. The advantage of them is that the footprint for the 2- 6 volt is almost the same as 1 12 volt. So for the same footprint you get twice the ah. NOt sure what density has to do with it. The advantage is more for the SIZE...irrespective of weight.


I didn't make it clear enough. I'm quantifying size and I think the statement "GC batteries have more capacity for their size" is misleading. It implies they have some inherent advantage. But it isn't true in terms of size and weight which are the only ways to truly quantify size. I also doubt they're cheaper but I didn't run those numbers.

Sure they may have more capacity for their footprint because they're taller. But it's not like taller is universally better. My two batteries are both in height contained locations where "size" most definitely includes consideration of the 3rd dimension. So in my case, 12V's give the most capacity possible for their "size".

I'm not knocking GC's at all. If they fit better in my boat I wouldn't hesitate to use them. But in terms of the numbers its basically a complete wash between GC's and regular 12V's.


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## chef2sail (Nov 27, 2007)

> Sure they may have more capacity for their footprint because they're taller. But it's not like taller is universally better. My two batteries are both in height contained locations where "size" most definitely includes consideration of the 3rd dimension. So in my case, 12V's give the most capacity possible for their "size".


Not necessarily so. My 4 Lifeline AGM 6 volts are the same height as most standard group 31. They deliver almost ah per volume than 1 group 31. I beleive the reason they weigh more is a heavier lead plate. The 4-6 volt batteries + 2 inches in length fit into the exact same space as the 2 group 31 I used to have.

Heres what you need to compare to compare apples to apples 2 - 6 volt GC vs 2 Group 31. Both will have approx the same ah. The two group 31s will take up substabtially more volume than the two golf carts. The weight difference is minimal ( 2X59.9 or 2X66)


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## asdf38 (Jul 7, 2010)

chef2sail said:


> Not necessarily so. My 4 Lifeline AGM 6 volts are the same height as most standard group 31. They deliver almost ah per volume than 1 group 31. I beleive the reason they weigh more is a heavier lead plate. The 4-6 volt batteries + 2 inches in length fit into the exact same space as the 2 group 31 I used to have.
> 
> Heres what you need to compare to compare apples to apples 2 - 6 volt GC vs 2 Group 31. Both will have approx the same ah. The two group 31s will take up substabtially more volume than the two golf carts. The weight difference is minimal ( 2X59.9 or 2X66)


Ok

GC10 = 794 square inches = 1.62 Wh per square inch
G31 = 833 square inches = 1.511 Wh per square inch

Ok so that's a 7% advantage for the GC battery in this case in terms of energy per volume. I'll agree that's not nothing. Although I know I've run these numbers in the past, for a different pair of batteries and seen the 12V's come out ahead like it does on weight in this case. I'll try to find that.


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## hellosailor (Apr 11, 2006)

"I know Deep Cycle batteries are not supposed to be starting batteries"
A common mistake. Deep cycle batteries are supposed to be deep cycle batteries. Starting (SLI) batteries are designed to be CHEAPER batteries with a MORE LIMITED PURPOSE and one special trick, high impulse discharges.
When you build a battery with thick plates, that physically limits how much impulse power those plates can put out, probably due to internal resistanace and heating. When you build lots of thin plates, you can put out lots of impulse power--as an SLI battery does. The problem with thin plates is that traditionally that compromises their physical strength, so they tend to fall apart and break down faster IF they are allowed to weaken (by discharging) in any significant way.
New result, a typical SLI battery can be destroyed by less than 6 deep discharges.
But if all you are doing is SLI (Starter, lights, ignition) service, an SLI battery may weigh and cost half of what a deep cycle battery does.

If your starting loads are small, as they are for most recreational marine engines, the average deep cycle battery can easily handle then without problems. Hell, I've started a Volvo MD7 with a 17AH "alarm and exit" type battery and neither one protested about it.

But if your engine is a 600hp Cummin Diesel, then sure, you may be better off paying closer attention to battery types and ratings.

Any deep cycle battery WILL have discharge ratings, and if you can't find them a quick call to the maker will tell you just how many amps that battery can safely provide in a surge for a starter motor. To put it in perspective, even a Group24 car battery will put out some 3000 Amps in a dead short, but the starter motor it is paired with usually draws one kilowatt or less (~100Amp) for all of 2-3 seconds.

So does the OP need deep cycle batteries? YES. Remember that SLI batteries have thin plates that easily take physical damage from discharge. They are designed, according to the folks I spoke to, for a MAXIMUM discharge of not more than 10%. At that point they start taking damage no matter how soon you recharge them. Ascompared to deep cycle batteries, that are designed for a30-50% typical discharge cycle.

Take an SLI battery, run the VHF all day, come home late and use the running lights, stay out for dinner and use the cabin lights, gee, doesn't the stereo sound great? and yes, you can and will damage an SLI battery with just day sailing, if you use the electronics. If you're not using much power, either one will certainly last the season, or two, maybe three. But the deep cycle won't cost much if anything more, and if will give you that extra margin for the weekend trips and longer days.


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## macswift (Jul 30, 2012)

My suggestion is to go back to first principles and calculate your daily 12v requirements, take account of your onboard charging facilities (engine alternator, and maybe solar panels and wind generator) and derive your battery requirement accordingly. Take a look at Understanding Boat Batteries and Onboard Electrics and it will guide you through the process.


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## Maine Sail (Jan 6, 2003)

asdf38 said:


> Ok
> 
> GC10 = 794 square inches = 1.62 Wh per square inch
> G31 = 833 square inches = 1.511 Wh per square inch
> ...


One thing this does not take into account is the cycle life of a 12V flooded battery vs. a 6V flooded battery when put in the same deep cycling application. The 6V batteries will outlast the 12V. I find on average 20-40% more life.

Beyond that on about 70% of the boats I work on "foot print" is the limiting factor and on about 30% height is the limiting factor.

GC2 / T105 size golf cart batteries are closer in foot print to a group 24 than a 27 or29/31 and with foot print usually being the constraint limit more so than height one must consider foot print comparisons vs. weight or box volume...

GC2 / T105 = 10 3/8" Long by 7 1/8" Wide by 10 7/8" Tall
Group 24 = 10 3/4" Long by 6 13/16" Wide by 8 11/16" Tall
Group 27 = 12 9/16" Long by 6 13/16" Wide by 8 3/4" Tall

If we compare the Deka / Duracell brand from Sam's Club (same as West Marine)

EGC2 6V = 230Ah for 2 batteries
Deep Cycle 24 12V = 150Ah for 2 batteries

The 6V batteries, in the same basic foot print of a group 24 have 80Ah more capacity for two, or nearly an entire group 24 battery... You also chose to compare weakest GC2 battery Deka makes at 215Ah/.. They also make that same case size in a 230Ah and 235Ah battery.

On boats where height is the limiting factor then 12V are often the only way to go unless you want to get spendy on Lifeline GPL-4CT's... But on boats where foot print is the limiting factor 6V batteries win hands down..

The OP really does not need much and a couple of group 24, 27 or 31's will do just fine. I would advise against the current crop of Wal*Mart batteries. Firstly they are labeled incorrectly and the labeling means NOTHING. It was clearly drawn up by a marketing department who knows squat. Secondly the new batteries are more of a dual purpose than the original Maax 29's that were actually built by US Battery and were an excellent product. I would instead look towards Wal*Marts sister store Sam's Club where in about 25 states they sell the Deka / East Penn brand of batteries.


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## asdf38 (Jul 7, 2010)

Maine Sail said:


> One thing this does not take into account is the cycle life of a 12V flooded battery vs. a 6V flooded battery when put in the same deep cycling application. The 6V batteries will outlast the 12V. I find on average 20-40% more life.


Right and I don't have any numbers to quantify life. And while I've heard people say that GC's last longer I've remained skeptical for three reasons: 
1) It's said that because they have less cells the plates are thicker. Fine but you could realize the same benefit by moving to larger 12V batteries. I've never seen/heard evidence of that.
2) The weight numbers I just ran through came out nearly 100% identical energy density by weight for the GC vs the 12V. That suggests, though doesn't prove, identical technology internally. (The volume numbers differed but volume factors in non-functional aspects like case design).
3) The applications are largely the same - why would Deka engineer better cycle life into their GC batteries than their marine batteries.

So do you have any data to point too on this?



Maine Sail said:


> You also chose to compare weakest GC2 battery Deka makes at 215Ah/.. They also make that same case size in a 230Ah and 235Ah battery.


Good point. I didn't notice that..If I have a chance I'll change my numbers previously. Obviously that helps the GC a lot in terms of volume. The weight of those larger capacity batteries does go up however.


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## Maine Sail (Jan 6, 2003)

asdf38 said:


> Right and I don't have any numbers to quantify life. And while I've heard people say that GC's last longer I've remained skeptical for three reasons:
> 1) It's said that because they have less cells the plates are thicker. Fine but you could realize the same benefit by moving to larger 12V batteries. I've never seen/heard evidence of that.


Actually you can't the plates are still thinner, on average 0.040 - 0.065 vs. .100 - .125, and footprint is again one of the biggest limiting constraints.



asdf38 said:


> 2) The weight numbers I just ran through came out nearly 100% identical energy density by weight for the GC vs the 12V. That suggests, though doesn't prove, identical technology internally. (The volume numbers differed but volume factors in non-functional aspects like case design).


Again, energy density is a totally meaningless figure because it does not take life cycles into account. You can have a 100Ah battery rated at 200 cycles and a 100Ah battery rated at 2000 cycles... No comparison..



asdf38 said:


> 3) The applications are largely the same - why would Deka engineer better cycle life into their GC batteries than their marine batteries.
> 
> So do you have any data to point too on this?


Actually the "applications" are not the same. For years the marine industry has used "hybrid" dual purpose style batteries that by true deep cycle definition are not really deep cycle batteries at all. They do make true deep cycle 12V batteries but your not buying them at WM or most marine stores.. Do they work? Sure, are they as optimal as 6V or 2V cells for a marine deep cycle application in terms of longevity, absolutely not..

So as for data yes I have hundreds of boats I work on, in the "real world", that show a 20 - 40% longer average life with 6V vs. 12V. I use the best analyzers money can buy, one is $2000.00 and the other was about $800.00 plus I have many other means of testing too. My Midtronics tool is the one battery manufacturersuse and supply to distributors like West Marine, Wal*Mart & Sam's Club for warranty claims.

Beyond that data you can always call Trojan and ask them for the cycle life at 50% DOD for the marine SCS series of 12V batteries vs. the Golf Car line. What they will tell you is that the SCS at 50% DOD is rated by Trojan at 600 cycles and the golf car batteries like the T105 are rated at 1200 cycles!!! Of course these are "lab" numbers and you'll never see that in the "real world" but you will see longer life out of 6V golf cart batteries vs. 12V in the same application.

Again that is DOUBLE THE CYCLE LIFE, per Trojan battery.... So yes the thicker plates, case design etc. do make differences. Remember that 6V battery has 3 cells and weighs 66 pounds vs. the 12V battery having 6 cells and weighing the same. Which battery has the thicker plates the one with 3 cells or the one with 6 cells?

I don't see the 50% differences in the "real world" but I do see 20-40% longer life "on average" out of true deep cycle golf car batteries vs. 12V "marine style" batteries.I measure this with industry standardized test equipment so this is not just a shoot from the hip thing... The differences are real, quantifiable and measurable differences and also backed up by companies like Trojan battery in their own in-house testing.

You can choose to believe or not... I see, touch, feel & measure so I believe....


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## asdf38 (Jul 7, 2010)

I just like to understand things well. And what I'm still missing is what's the downside to the GC's? We've established they have have longer life and more energy per volume...but what are they missing? It's got to be something otherwise these companies are just selling second rate products with "Marine" stamped on them...

They must think thinner plates have some advantage in the marine environment, is it still cranking amps? Are our Duracell Deka deep cycles still designed to provide cranking amps? They are rated for that while the GC's arn't.


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## SloopJonB (Jun 6, 2011)

hellosailor said:


> "I know Deep Cycle batteries are not supposed to be starting batteries"
> A common mistake. Deep cycle batteries are supposed to be deep cycle batteries. Starting (SLI) batteries are designed to be CHEAPER batteries with a MORE LIMITED PURPOSE and one special trick, high impulse discharges.
> When you build a battery with thick plates, that physically limits how much impulse power those plates can put out, probably due to internal resistanace and heating. When you build lots of thin plates, you can put out lots of impulse power--as an SLI battery does. The problem with thin plates is that traditionally that compromises their physical strength, so they tend to fall apart and break down faster IF they are allowed to weaken (by discharging) in any significant way.


So regular automotive batteries are sprinters and deep cycle batteries are marathon runners?


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## MedSailor (Mar 30, 2008)

asdf38 said:


> I just like to understand things well. And what I'm still missing is what's the downside to the GC's? We've established they have have longer life and more energy per volume...but what are they missing? It's got to be something otherwise these companies are just selling second rate products with "Marine" stamped on them...
> 
> They must think thinner plates have some advantage in the marine environment, is it still cranking amps? Are our Duracell Deka deep cycles still designed to provide cranking amps? They are rated for that while the GC's arn't.


The golf cart battery is the most widely sold size of battery if I recall correctly. They're mainly used in forklifts. One downside is that they require twice as many connections and thus have twice as many cables and potential rust points. More places to maintain.

For deep cycle applications they generally ARE considered better by the likes of us. On the other hand, if you want a deep cycle for your 14ft fishing boat's trawling motor, you don't want to disconnect 2 golf carts and lift the two of them out daily as you charge them. The other batteries have their uses and for many the need for deep repeated cycles isn't crucial.

As in your case, where you'd be just fine with any size deep cycle for your house battery and any size deep cycle or starter for your starting bank.

MedSailor


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## asdf38 (Jul 7, 2010)

Ok well the answer is in. According to Trojan, as Mainsail said, Golf Carts will have almost 50% longer life. The tradeoff, as I suspected, is in cranking amps - apparently even the deepest "Marine Deep Cycle" battery is still designed with cranking performance in mind.

This comes directly from Trojan tech support when I asked them specifically about the differences between their SCS200 G27 and T-105 Golf Cart batteries. Credit to Trojan for the quick response.

I'll say that I find it disappointing, and counter-productive that manufactuers don't make these tradeoffs clear. There are a ton of marine buyers who want nothing but the very best deep cycle performance and published literature makes no note of these lifetime tradeoffs.

Anyway, as far as I'm concerned the verdict is in. I have little doubt that a normally sized golf cart house bank can start any engine in it's sailboat. So...

*Never buy a marine battery for your boat unless you absolutely can't fit a GC.*


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## Minnewaska (Feb 21, 2010)

asdf38 said:


> .....*Never buy a marine battery for your boat unless you absolutely can't fit a GC.*


Not so fast. I have nearly 20 batteries aboard and can't either take them off or keep them routinely charged over the winter. AGM or Gel are the only way for me. I have the later for my house bank, as the charging system was spec'd that way from the factory. All others are AGM, expect one. The dinghy start battery is a plane old maintenance free tractor battery. It was $30 and I'm happy to buy a new one every year, compared to the cost of a marine battery. This winter is the first experiment with it. One season is breakeven, two seasons is a winner. For $30 and breakeven chances, I'm willing to go for it. Not on a house of golf carts.


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## Maine Sail (Jan 6, 2003)

asdf38 said:


> Ok well the answer is in. According to Trojan, as Mainsail said, Golf Carts will have almost 50% longer life. The tradeoff, as I suspected, is in cranking amps - apparently even the deepest "Marine Deep Cycle" battery is still designed with cranking performance in mind.
> 
> This comes directly from Trojan tech support when I asked them specifically about the differences between their SCS200 G27 and T-105 Golf Cart batteries. Credit to Trojan for the quick response.
> 
> ...


And even two T105's or similar will still start a large Cummins even on the coldest winter days. We had a 300HP Cummins in our old power boat. Started easily with two T105's...









This is one of my power boat customers who is also a sailboat customer. He takes his batteries and charging as seriously on his twin screw power boat as he does on his blue water cruiser that has been across the Atlantic and beyond about 6 times..









These 4 6V batts start the twin screw/engine 6 cylinder turbo Volvo's @ 260HP each, with zero effort. The engines start in 0.75 seconds as measured with my Midtronics analyzer.... He starts both motors off the house bank down to 50% SOC easily....

So yes, as I have been saying, unless you can't fit the height of 6V batteries they are the best bang for the buck..


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## SloopJonB (Jun 6, 2011)

Maine Sail said:


> /QUOTE]
> 
> Wow!


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## blt2ski (May 5, 2005)

Most manufactures will state that some Deep cycle lead 6V batteries will get about twice the discharges etc vs and equal sized 12V be it lead, agm or gel. At the end of the day, it really depends upon how much you want to spend, what your charging system has to charge the batteries. Does not do any good to put in AGM's if you have a smallish alternator as and example, as the batteries may take more than the alternator can produce, and blow it up!

Then one has to decide how much and often the batteries will be discharged, rate etc, as to what amount of house bank one needs. I've frankly done well with a single size 24 for the last 6 yrs. But, I mostly day sail, rarely anchor out and need upwards of 24 hrs of power, for a fridge (I have an ice chest), few lights, running lights, st60+ guages, and radio. Very little power useage! Hence why I could see the OP using a single 24 as a starting battery, and another 24 in a DC style for the house battery! If he needs a bit more, there are some 24's with up to 90ahr vs the typical 70-75. Or go to a 27 with around 85-90, and some of the higher led content to 105!

This battery what you should have or not is almost as bad as anchor option!.....well, maybe on par with sailcloth options or a bit worst.......

Marty


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## SlowButSteady (Feb 17, 2010)

My boat has two 6V GC batteries (got them at Costco; they have similar specs to T-105s, but I'm under no illusions about them being "as good as" T-105s) as the "main" bank, and a 50 ah "wheelchair" AGM battery (got it at Sears) as the "reserve" bank. Either bank will start the 2gm20, no problem. I normally use the main bank for everything (starting and deep-cycle usage), with the AGM being there "just in case" (but I never really _needed_ it, yet). All the charging inputs (alternator, solar, shore power) are connected to the "main" bank with a battery combiner, that has a AGM setting for the reserve bank, interconnecting the two banks. The access to the batteries on my Cal 2-27 is rather insane, so muscling anything bigger than the golf cart batteries into place would have been out of the question. The capacity of the GC batteries is probably over-kill for my boat. But I NEVER have to seriously worry about draining the batteries too much.


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## MedSailor (Mar 30, 2008)

Maine Sail.

I want you to know that *your post has been flagged for the moderators.*. There is no posting of porn pictures allowed on SailNet.



















MedSailor


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## cherev (Sep 6, 2000)

I suggest two banks of two 6v golf cart batteries for house use, and two 6v golf-cart starting batteries.

If you have the space, which I do on a Morgan 41' OI, use eight 6v golf-cart batteries for the house, wired so serial pairs provide 12v to bus lines. Golf-cart batteries are relatively cheap, and can be found everywhere. Plus you can maintain, test, and trade them out yourself anywhere without any giant hassle.

Lots of juice is important if you have women aboard and an inverter.


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## SloopJonB (Jun 6, 2011)

Minnewaska said:


> Not so fast. I have nearly *20 batteries* aboard


Yowza!  Don't you think it might be time to consider a gen set?


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## Minnewaska (Feb 21, 2010)

SloopJonB said:


> Yowza!  Don't you think it might be time to consider a gen set?


Have a genset for sure.

House... 4 batts
Winches... 2 batts
Windlass... 2 batts
Bow thruster.... 2 batts
Main start... 1 batt
Genset start.... 1 batt
Dinghy start... 1 batt

Think I overshot with 20, but 13 still makes the point.


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## mitiempo (Sep 19, 2008)

Minnewaska said:


> Have a genset for sure.
> 
> House... 4 batts
> Winches... 2 batts
> ...


I am curious how they are all charged! It could have been accomplished with less batteries and good cabling.


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## tommays (Sep 9, 2008)

I am pretty sure










You use to have something like this (two group 27s)

They have much better custom hold downs NOW 

Two is good just because of things like having TWO bilge pumps on different 24 hour circuits on each battery just in case 


















And ACR with a small solar control keeps the whole deal happy and I NEVER need to run the motor as are weekend needs are some led cabin lights


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## Minnewaska (Feb 21, 2010)

mitiempo said:


> I am curious how they are all charged! It could have been accomplished with less batteries and good cabling.


Since the house is 12v and the winches, windlass and thruster are 24v (hence the 2 12v batt each), it would be difficult to gang too many together. Have separate banks for the 24v systems allow redundancy. Who would want to get back to the dock and find the thruster is dead.....  

To combine some of these would require running some battery cables 20 feet or more. That's not a good idea.

All but the genset start have shore powered chargers that can obviously be powered with the genset too. The main alternator will charge the house and main start.


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## SloopJonB (Jun 6, 2011)

Minnewaska said:


> Since the house is 12v and the winches, windlass and thruster are 24v (hence the 2 12v batt each), it would be difficult to gang too many together. Have separate banks for the 24v systems allow redundancy. Who would want to get back to the dock and find the thruster is dead.....
> 
> To combine some of these would require running some battery cables 20 feet or more. That's not a good idea.
> 
> All but the genset start have shore powered chargers that can obviously be powered with the genset too. The main alternator will charge the house and main start.


Cap'n Nat & LFH must be up to several hundred RPM in their graves.


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## Capt Len (Oct 9, 2011)

Beets me how I ever sailed away with oil fired nav and compass lights. Mind you, at only 22 tons I could easily weigh anchor by armstrong and sail up to a dock.


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## blt2ski (May 5, 2005)

Along with the OP has not been heard from since day one!

maybe over his/her head!?!?!?!?!???

Marty


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## Navigator Wannabe (Nov 4, 2012)

Perfect for your use, I had the same on a 27-footer.
I had two batteries that Costco sold as Marine batteries, i.e. slightly more robust automotive starting batteries, even smaller than the ones you linked to, I think about 60 Ah, $50 each.
Works perfect for day sailing and weekends. 
A switch separating the two batteries is good to make sure you always have power to start in the morning.
Run one somewhat empty, but leave enough power to start, then use the other one. IF you run it empty over night, you can still start, and use almost all capacity.

And before the yaddaing by 'battery experts' starts: 
Automotive starter batteries (which these are, in essence) DO survive the running REALLY low on occasional weekend use very well, for practical purposes. They last years. 
Shorten theoretical battery lifetime by 50%, and you still have several years of use, and are out of $50. 
As proven by people who have to jump-start their cars. 



chartscharts said:


> All,
> 
> My CAL29 is in need of new batteries. The existing ones are shot and won't hold a charge. I wanted to solicit opinions about downsizing drastically.
> 
> ...


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## chartscharts (Aug 1, 2006)

blt2ski said:


> Along with the OP has not been heard from since day one!
> 
> maybe over his/her head!?!?!?!?!???
> 
> Marty


Not all over my head! 

Enjoying the great replies and reading them closely. Sounds like the consensus is that I can get away with a much smaller set up. I am intrigued by the GC battery idea, but think I'm going to go with the simpler project of swapping 12v batteries with smaller/cheaper new ones. Then at least I'll keep a charge overnight!

-Charts


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## Minnewaska (Feb 21, 2010)

Safest would be to use the same style. If current are flooded, get flooded. If AGM, get AGM, etc.

Your charging system should already be designed for which you have. The wrong combo can kill the new batts.


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## chartscharts (Aug 1, 2006)

Well, I ended up buying two Everstart Marine 29DC (selection #95), 845 marine cranking, [email protected] batteries. This afternoon I loaded them up on the boat, and took out the old ones.

Taking out the old ones involved a lot bumps, scraps, lots of ropes, block and tackle, a metal bar across the top of the companion way, etc etc...

I can't believe I got them out! They're in the cockpit now. Need to figure out how to get them off the boat. I can't see slinging them in/out of my dinghy like I did the new ones. 

Probably need to enlist some strongbacks.

I'll post again with how the batteries work out.

-Charts


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## bljones (Oct 13, 2008)

Now you need to repaint your waterline.


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## chef2sail (Nov 27, 2007)

> I can't believe I got them out! They're in the cockpit now. Need to figure out how to get them off the boat. I can't see slinging them in/out of my dinghy like I did the new ones.


Pull up to dock. Block and tackle off the end of the boom and lift and swing boom over the dock and drop

Dave


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## Minnewaska (Feb 21, 2010)

chartscharts said:


> Well, I ended up buying two Everstart Marine 29DC (selection #95), 845 marine cranking, [email protected] batteries.


Something is fishy. Industry standard is to rate batteries at a 20hr discharge rate. 1amp discharge suggests these batteries would last 122hrs, but if you increase the draw to 2amps, the hours drop by more than half due to resistance.

Increase the draw to a fairly light 5 or 6 amps and, while the linear math would suggest 20+ hours, I'm sure it would be substantially less. Maybe only a few hours.

Further compound this by best practice not to draw your batteries down by more than 50% of their capacity for longest life and these sound like they may be a little light.

Going to one or two smaller batteries sounded like a good idea, its just that something doesn't sound right about these, if they are advertised at 1amp. There are some battery gurus around here that may know better than I.


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## Maine Sail (Jan 6, 2003)

Minnewaska said:


> Something is fishy. Industry standard is to rate batteries at a 20hr discharge rate. 1amp discharge suggests these batteries would last 122hrs, but if you increase the draw to 2amps, the hours drop by more than half due to resistance.
> 
> Increase the draw to a fairly light 5 or 6 amps and, while the linear math would suggest 20+ hours, I'm sure it would be substantially less. Maybe only a few hours.
> 
> ...


As I mentioned in an earlier post the Ah rating on those batts is meaningless. Likely a BAD mistake by the marketing department... Problem is no one at Wal*Mart knows the correct specs....


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## Minnewaska (Feb 21, 2010)

Maine Sail said:


> As I mentioned in an earlier post the Ah rating on those batts is meaningless. Likely a BAD mistake by the marketing department... Problem is no one at Wal*Mart knows the correct specs....


Ohhhhh, Wallyworld batteries. It will be interesting to hear how they make out in year 2.


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## Maine Sail (Jan 6, 2003)

Minnewaska said:


> Ohhhhh, Wallyworld batteries. It will be interesting to hear how they make out in year 2.


Mine are going on year six......

However my Wal*Mart batteries were made by US Battery for Johnson Controls who then sold them to Wal*Mart. US Battery makes excellent quality batteries, some of the best "12V marine" batteries, & 6V, other than Trojan..

Wal*Mart has since sourced a less expensive replacement for the batteries I have and they are NOT the same. I can't however comment on the longevity because I stopped using them due to the "lack of a clue" about batteries that Wal*Mart exhibits. Sam's Club, the sister company, took on Deka/East Penn so that is a HUGE + !!

*6 Year Wal*Mart Battery Observations*


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## Minnewaska (Feb 21, 2010)

Maine Sail said:


> Mine are going on year six......


And, no doubt, the version you purchased weren't rated at 1amp or you would have run.


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## Maine Sail (Jan 6, 2003)

Minnewaska said:


> And, no doubt, the version you purchased weren't rated at 1amp or you would have run.


Correct. The problem is the batteries the OP bought are also not rated at 1A, though that is what it says. It makes NO SENSE...

I suspect they are a 95-115Ah battery at the 20 hour rate. There are only a few group 31 batteries that approach 125 - 130 Ah's legitimately and US Battery and Trojan are two of those suppliers.. As an example the Deka group 31's are 105Ah and the Trojan SCS 225 and US Battery DCXC31 is also 130Ah's...

Still none of these 12V batts will last as long as a 6V. If you can fit 6V they are almost always the best bet and best bang for the buck. Still our "Wal*Mart" batteries have cost us about $29.94 per year of service for the entire bank.... Pretty cheap energy....


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## peterchech (Sep 2, 2011)

Mainesail, those were the deep cycle ever starts that u got from Walmart, correct? They are everstarts, right? Because they still sell them here by me.

I need a new battery for one of my banks, I have had a walmart everstart for about a year now and it does the job so far, but I'm very suspect about anything Walmart sells, quality wise. I was thinking to get an optima for the bank, as I have heard really good things about optimas, but it is $200 compared to less than half that for an ever start dc or similar. What do you think about the optimas? Are the everstarts here:EverStart 27DC-6 Marine Battery: Automotive : Walmart.com the same ones that you tested over the 6 years?


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## Maine Sail (Jan 6, 2003)

peterchech said:


> Mainesail, those were the deep cycle ever starts that u got from Walmart, correct? They are everstarts, right? Because they still sell them here by me.
> 
> I need a new battery for one of my banks, I have had a walmart everstart for about a year now and it does the job so far, but I'm very suspect about anything Walmart sells, quality wise. I was thinking to get an optima for the bank, as I have heard really good things about optimas, but it is $200 compared to less than half that for an ever start dc or similar. What do you think about the optimas? Are the everstarts here:EverStart 27DC-6 Marine Battery: Automotive : Walmart.com the same ones that you tested over the 6 years?


Wal*Mart no longer sells the US Battery product. The case looks like this:










This was a customers battery who switched to AGM. It is also a 2007 and still good. It is the same exact battery I have on our boat and is a US Battery group 31..









If you can find a US Battery distributor the US Battery DCXC-31 is a great battery and I find it even better than the Trojan SCS-225 in terms of average longevity:









The DCXC 31 was specifically designed for the floor scrubber industry and has plates nearly as thick as a GC battery at .100. It is about as close to a true "deep cycle" battery you're going to get in group 31 case....


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## hellosailor (Apr 11, 2006)

Peter-
Optima batteries are in a world of their own. They are made by JCI, who are a top maker. They are sprial-wound AGM batteries, and in theory that process makes them much cheaper to build than flat-plate batteries, and more vibration resistant. In practice, JCI charges about a 30-40% premium for them, and because you have round batteries in a rectangular case, you also get about 10% less capacity than a same-size flat plate battery.
And, no better warranty.

If AGM is the way you want to go, I'd go with flat-plate AGM batteries, get 10% more capacity at 30% less price. Last year...I think that was about $200? $230? for a G31 from various sources. Of course the price of lead seems to double almost weekly, for reasons that totally elude me.

And if your charging system can match the, consider gel batteries. Even the AGM-makers are now saying gel batteries will totally outperform AGMs in terms of charge cycles, if you can give them everything else they want.

But Optimas? Mainly, they've been _branded _very nicely. If JCI would just drop the price and raise the warranty, to match what they say about the technology...


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## Maine Sail (Jan 6, 2003)

hellosailor said:


> Peter-
> Optima batteries are in a world of their own. They are made by JCI, who are a top maker. They are sprial-wound AGM batteries, and in theory that process makes them much cheaper to build than flat-plate batteries, and more vibration resistant. In practice, JCI charges about a 30-40% premium for them, and because you have round batteries in a rectangular case, you also get about 10% less capacity than a same-size flat plate battery.
> And, no better warranty.
> 
> ...


It should be noted that JCI bought this brand from EnerSys who invented the Optima's. JCI does not manufacturer all their own batteries and many of the "brands" they have purchased. They still buy batteries from companies like US Battery in certain sizes and then private label them.

EnerSys sold the brand because they had a much better designed AGM in the Odyssey thin plate, pure lead battery. The Odyssey batteries are quite amazing in the current they can both take and deliver but still don't quite have the cycle life of a decent deep cycle flooded or GEL. I have personally watched a 400Ah bank of Odyssey batteries take 130A+ for nearly an hour or everything the alt could throw at them.. They would have taken more if we had it...

It should also be noted that the spiral cells cost you a lot more than 10% in Ah capacity if you compare case size for case size as in the group 31 batteries below..

A group 31 Optima Blue Top AGM is *75Ah*
A group 31 Lifeline AGM is available in either 105Ah or 125Ah capacities
A group 31 Deka AGM is 105Ah
A group 31 Odyssey AGM is 100Ah
A group 31 Trojan wet cell is 130Ah
A group 31 US Battery wet cell is 130Ah
A group 31 Deka/West Marine/Sam's Club/NAPA wet cell is 105Ah

Even the absolute lowest Ah capacity flat plate batteries is has 25% more capacity than an Optima group 31 and the largest has 43% more capacity..... Big differences!!!


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## miatapaul (Dec 15, 2006)

hellosailor said:


> Peter-
> Optima batteries are in a world of their own. They are made by JCI, who are a top maker. They are sprial-wound AGM batteries, and in theory that process makes them much cheaper to build than flat-plate batteries, and more vibration resistant. In practice, JCI charges about a 30-40% premium for them, and because you have round batteries in a rectangular case, you also get about 10% less capacity than a same-size flat plate battery.
> And, no better warranty.
> 
> ...


I must say I had an Optima in my Miata and it lasted 10 years. It even started the car after sitting for 2 years without being jumped. But on a boat? I think I would stay with wet cells.


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## hellosailor (Apr 11, 2006)

I can't see that wet cells vary from 105 to 130Ah in the same size group. IIRC a G31 was "always" rated around 100Ah ten years ago, and no one has made astonishing breakthroughs in chemistry, meaning they'd have to thin the case walls down to stuff in 30% more plates.

Dunno, Maine, but it smells like someone is using a rubber ruler to get some of those numbers. Have you done any cycle testing to see how those numbers play in the real world? I just can't see a full 1/3 difference in capacity being real.

Paul-
When Miata was a big new thing, AGM flat plate batteries were almost unheard-of, which may be why Mazda used the Optima. Or, again remembering the time frame, someone could have cut them a loss-leader deal to promote the brand. But Mazda learned a big lesson from Fiat: Wet lead battery in trunk means big time corrosion problems from acid vapors. BMW currently puts wet lead acid in the back of the X3/X5, but of course they found a superior (cough) way to engineer it, with a little breather hose to vent the battery under the car. So it can rot out the underbody instead.<G>

I only got 8 years from my last abused AGM. In which time I think the prices doubled. (Ouch!)


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## Maine Sail (Jan 6, 2003)

hellosailor said:


> I can't see that wet cells vary from 105 to 130Ah in the same size group. IIRC a G31 was "always" rated around 100Ah ten years ago, and no one has made astonishing breakthroughs in chemistry, meaning they'd have to thin the case walls down to stuff in 30% more plates.


The Trojan SCS-225 has been around a long time at 130Ah's and the US Battery DCXC 31 about 10 years. Lifeline recently added the 31XT to the line up. It all has to do with the lead, paste grid design etc. etc... US Battery is using the same paste and design they use in their GC batts in the group 31 because they sell them to a huge floor scrubber company who demanded more cycle life.. While a bit more expensive than a typical group 31 they are still less than the Trojan SCS-225.

Group 31 cases are not the only case size to have variances. The 6V GC2 batts range from 200Ah to 240+Ah's all in the same case...

I have capacity tested the SCS-225 and the US DCXC 31 and both meet the Ah rating at least at year one (US SCXC 31) and year two (SCS-225)

Our US Battery/Wal*Mart batteries came within a few Ah's of their 125Ah rating at year 5.....

This is what my 5 year old US Battery group 31's put up during a 20 hour capacity test. They were rated at 125 Ah's:

Battery #1 = 117.7Ah @ 5 years old
Battery #2 = 118.3 Ah @ 5 years old
Battery #3 = 117.9 Ah @ 5 years old


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## peterchech (Sep 2, 2011)

Yeah the Optimas are very expensive, considering that they are only 54 ah @ 20 hours for a group 27 battery...

I just have a hard time finding anything better locally... autozone has duralasts







any thoughts on this brand?


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## chartscharts (Aug 1, 2006)

Well my new batteries have held a charge for 3 days! That's a land speed record compared to my kaput banks.

Speaking of the kaput batteries. I found a local company that will come pick them up and give me $20 bucks each for them. I've never tried recycling batteries for cash. Is this a reasonable amount?

If not, anyone know of a San Diego company that will do better?

-Charts


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## hellosailor (Apr 11, 2006)

Reasonable? Dunno about Cali but in most states the "mandatory" surrender fee is about $9 when you turn in old batteries while buying new. And then you've got to drag them in. to find someone willing to come fetch? Priceless.

Heck, Cali is the state that made lead wheel weights illegal, be glad they don't send the Lead Police out to supervise you while you've got excess batteries on your premises.


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## hj0516 (Jan 23, 2012)

I have read that it is better to have two 6 volt batteries in parallel rather than one 12 volt, but at twice the cost is the benefit twice as much. At about the same cost you could have two 12 volt batteries and would that be better that two 6 volt??
I am talking about deep cycle for house bank needs, I have 4 golf cart batteries now and cruise every weekend and in the marina it is on charger. I also have twin solar panels and a wind charger. Plan next year to cruise and anchor out a week or two at a time.
Any suggestions on which way is better?? Also have separate starting bank. Thanks for any help.
sailor0516


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## asdf38 (Jul 7, 2010)

"but at twice the cost is the benefit twice as much"

I think you may be misunderstanding the numbers. 6 volt batteries will have twice the amp-hour capacity of a similar size and cost 12V. When you wire two 6V's in series you get a bank that's very similar to two 12V's in parallel in every aspect including size, cost and weight.

Where the advantages come in are mostly in overall lifetime. Golf Cart batteries are designed to be truly deep cycled and last longer than "Marine Deep Cycles" in this application. Marine batteries, even good "Deep Cycle" ones still compromise lifetime for cranking amps. This is unfortunate and leads to lots of confusion over this issue (see my posts earlier on in this thread..)

Just to be clear, the advantages of the GC batteries have little or nothing to do with the fact that they are 6V. It's that they are one of the easiest to find suitable true deep cycle batteries and the fact that they are 6V is a coincidence. As Mainsail has pointed out, full deep cycle 12V's exist but are harder to come by. By itself 6V is actually a small disadvantage because of the added wiring complexity. But the longer life, increased capacity, low cost and often better form factor (taller and narrower) of GC's often make up for this.


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## Maine Sail (Jan 6, 2003)

hj0516 said:


> I have read that it is better to have two 6 volt batteries in parallel rather than one 12 volt,


Two 6V batteries in PARALLEL make a 6V bank. Two 6V batteries in SERIES makes a 12V bank..



hj0516 said:


> but at twice the cost is the benefit twice as much.


Actually $$$ to Ah's 6V batteries are less costly. The typical GC2 6V golf cart batteries will yield about 225 - 240 Ah's and almost always for less money than 12V batteries. To equal that capacity in 12V would run you more $ for two 12V batts and take up a larger footprint.

Here's an example from the same retailer:

Group 24 12V Deep Cycle 75Ah = $69.76 X 2 = 150Ah's = $139.52 = 93¢ Ah
Group 27 12V Dep Cycle 90Ah = $77.76 X 2 = 180Ah's = $155.52 = 86¢ Ah
Group 31 12V Deep Cycle 105Ah = $84.67 X 2 = 210Ah's = $169.34= 81¢ Ah
GC2 6V Deep Cycle 215Ah = $78.83 X 2 = 215Ah's = $157.66 = 73¢ Ah
EGC2 6V Deep Cycle 230Ah = $88.74 X 2 = 230Ah's / $177.48 / 77¢Ah



hj0516 said:


> At about the same cost you could have two 12 volt batteries and would that be better that two 6 volt??


No, it would not be better in terms of either cost or longevity.. One thing the above cost example leaves out is that 6V golf cart batteries will survive many, many, many more "cycles" than a deep cycle 12V battery. Trojan for example says up to 50% more cycles that their 12V brethren. So not only are they cheaper on a $$ to Ah scale but they will also outlast a 12V battery too making the $$ to Ah conversion but a small piece of the cost analysis....



hj0516 said:


> I am talking about deep cycle for house bank needs, I have 4 golf cart batteries now and cruise every weekend and in the marina it is on charger. I also have twin solar panels and a wind charger. Plan next year to cruise and anchor out a week or two at a time.
> Any suggestions on which way is better?? Also have separate starting bank. Thanks for any help.
> sailor0516


Stick with what you have. You have a series parallel bank that will outlast just about any12V configuration that would fit in that foot print and you have it for less money..


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## sstuller (Nov 1, 2000)

The one virtue of the 12 volt battery is voltage. You are getting twice the voltage for half the weight. Two 6 volt GC's weigh about 120# for 12 volts while the 12 volt battery is 60#. If you want 24 volts two 12 volt batteries weigh 120 # but you need four GC's at 240# to get 24 volts. Usually sailors worry about weight. Unless you absolutely need the extra capacity from the GC's, 12 volt batteries have the weight advantage. Thanks. Steve S.


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## Paddyd (Jun 14, 2012)

down sizing for your needs is a great option , I would put in qtty 2 f27 deep cycle 750 cranking amps batteries maintenance free and then put on a Sunforce 5w solar panel 
for your needs this would more than meet your goals


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## Maine Sail (Jan 6, 2003)

sstuller said:


> The one virtue of the 12 volt battery is voltage. You are getting twice the voltage for half the weight. Two 6 volt GC's weigh about 120# for 12 volts while the 12 volt battery is 60#. If you want 24 volts two 12 volt batteries weigh 120 # but you need four GC's at 240# to get 24 volts. Usually sailors worry about weight. Unless you absolutely need the extra capacity from the GC's, 12 volt batteries have the weight advantage. Thanks. Steve S.


Steve,

For sailboats there is no weight advantage when you are talking 12V batteries, unless the ONLY factor you include in the equation is the weight. You don't buy batteries by weight however, you by them by your consumption needs or Ah capacity for your planned use.

The the 120 pounds of 6V will be giving you 225 - 240 Ah's and the 60 pounds of 12V will be giving you just 105Ah's... That is less than half the capacity and roughly half the cycles. When you cut the capacity you also cycle the batteries deeper thus also shorten battery bank life.

When comparing weight it is best to compare Ah's to pounds based on price, consumption needs, cost, charging capacity and life cycles...

6V batteries are heavier because they have thicker lead plates. Because of this, they last longer. They also very often have more Ah capacity per pound than 12V making 12V batteries heavier for the same Ah capacity.. When you get to equal Ah's capcity a 12V battery the weight differences are negligible but the life span is not.

So for a 450Ah bank there may be 10 pounds difference, either way, but multiple years & cycles difference in battery bank longevity..

If you look at "foot print" a group 24 is roughly the same as a GC2 6V in the floor space it requires..

Four 6V GC2 batteries will give you 450Ah's and weigh roughly 260 pounds.

It takes SIX group 24 12V batteries to equal the Ah capacity of 4 6V batteries.

Those SIX group 24 batteries weigh 270 pounds or 10 pounds MORE for the same Ah capacity. You weigh more yet you will have a LOT shorter battery bank life with this ten pound heavier 12V bank than you would with 4 6V GC2's..

Weight to Ah's..

450 Ah's GC2 6V = 260 Pounds (4 batteries) 
450 Ah's G-27 12V = 265 Pounds (5 batteries)
450 Ah's G-24 12V = 270 Pounds (6 batteries)

There are very few boats today over 30 feet that can get away with a single 60 pound/100Ah battery, (35 usable Ah's when cruising), and not be replacing it every other year or sooner. People are simply using a lot more power today than they did even 10 years ago..


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## hellosailor (Apr 11, 2006)

Well Steve does hava a point. If all you care about is _volts _and _weight_, you buy a #23A twelve volt alkaline remote control battery. Twelve volts, that's all that's important. Doesn't need any of that charging equipment, and weighs only about a half ounce, too. Much lighter and smaller and cheaper than those expensive lithium-whatever batteries too.

Best of all you can carry a spare one in the remote control on your key chain! About a buck and a half at most drug and hardware stores.

He's got a point, Maine.


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## chef2sail (Nov 27, 2007)

hj0516 said:


> I have read that it is better to have two 6 volt batteries in parallel rather than one 12 volt, but at twice the cost is the benefit twice as much. At about the same cost you could have two 12 volt batteries and would that be better that two 6 volt??
> I am talking about deep cycle for house bank needs, I have 4 golf cart batteries now and cruise every weekend and in the marina it is on charger. I also have twin solar panels and a wind charger. Plan next year to cruise and anchor out a week or two at a time.
> Any suggestions on which way is better?? Also have separate starting bank. Thanks for any help.
> sailor0516


2 6 volt batteries = 220 ah at 12 volts

2 12 volt group 31 batteries have 220 ah at 12 volts

2 6 volt batteries ahs the footprint basically as 1 group 31

2 6 volts = same ah for 1/2 the space


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## sstuller (Nov 1, 2000)

Most boats on the water are less than thirty feet. Relative to displacement the difference between 60# and 120# is not significant for a thirty footer. As the boat gets smaller the battery weight is still the same and their weight does make a difference. Thanks. Steve S.


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## asdf38 (Jul 7, 2010)

Maine Sail said:


> There are very few boats today over 30 feet that can get away with a single 60 pound/100Ah battery, (35 usable Ah's when cruising), and not be replacing it every other year or sooner. People are simply using a lot more power today than they did even 10 years ago..


I'm sure this is true. However one thing in the back of my mind when discussing/reading bank life discussions is - does it matter?

At the end of the day batteries, especially lead acids are actually pretty cheap compared to everything else on a boat. If for space or weight reasons you don't want to add batteries it's not unreasonable in my opinion to decide that you'll just replace them every 2 or 3 years.

Personally I expect to get plenty of life out of my batteries and put a lot of thought into my system. But with $120 of batteries compared to ~4k fixed yearly expenses plus maintenance and discretionary it's not going to matter a lot in the big picture.


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## hellosailor (Apr 11, 2006)

$120...What's that buy, 120 AA cells or two el cheapo Group 27's?

I'm starting to look at battery longevity being a better _investment _than anything the broker can offer. I'm almost afraid to ask where I can find annual battery price information for the past ten years because I *know* what out of pocket has been.


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## asdf38 (Jul 7, 2010)

hellosailor said:


> $120...What's that buy, 120 AA cells or two el cheapo Group 27's?
> 
> I'm starting to look at battery longevity being a better _investment _than anything the broker can offer. I'm almost afraid to ask where I can find annual battery price information for the past ten years because I *know* what out of pocket has been.


Sams club 24 and 27. Ok maybe it was $135 and I didn't include the disposal fee. But there were no taxes in NH...

If you want to invest in my batteries I'm open to offers.


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## blt2ski (May 5, 2005)

asdf38 said:


> I'm sure this is true. However one thing in the back of my mind when discussing/reading bank life discussions is - does it matter?
> 
> At the end of the day batteries, especially lead acids are actually pretty cheap compared to everything else on a boat. If for space or weight reasons you don't want to add batteries it's not unreasonable in my opinion to decide that you'll just replace them every 2 or 3 years.
> 
> Personally I expect to get plenty of life out of my batteries and put a lot of thought into my system. But with $120 of batteries compared to ~4k fixed yearly expenses plus maintenance and discretionary it's not going to matter a lot in the big picture.


This is actually pretty true depending upon what and how you use the boat. I'm 28' on deck, just a skoosh under 30', the OP's boat is from the same era
but a foot or so longer......reality is, for how I use my boat, electronics on it, a single 85ahr batter worked fine! I can get upwards of 24-36 hrs of power out of it. Then again, all I am powering is house lights, running lights and some ST60+ instruments and radio. One does not need a lot of power to do this. Now if you are running GPS, chart plotter, fridge plus a few other things ON TOP of some of the basics if you will on a boat, then yes, one needs more wt in battery pack to function at a reasonable length of time.

Once you get to the a single 12V or two is too small, then as noted by some, 2 6V lead cells frankly is the best bang for the buck/wt ratio to supply your power needs. This is true from land yacht experience, along with water yacht experience.

For either application, it does no one any good to have as in the OP's case 2 150lb batteries, if he only needs a single 12V 65-100 lbs one to serve his needs. At the end of the day, one needs to decide battery sizing based on ones OWN needs, not mine, nor mainsails, nor smackies, CD's etc.

Marty


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## hj0516 (Jan 23, 2012)

Thanks to everyone for your info, sounds like I replace with 6v like I have already.
Boat is new to me and survey said the batteries would need replacing within year. At least I know what to look for and thanks again.
sailor0516


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## Maine Sail (Jan 6, 2003)

asdf38 said:


> I'm sure this is true. However one thing in the back of my mind when discussing/reading bank life discussions is - does it matter?


No it does not matter, until it does matter. Every summer I gain customers who've had batteries fail them at a bad time or leave them stranded. Some times these mishaps get expensive. One of my customers had it happen in a location where the tow cost was multiple times what a properly sized battery bank would have been. He had a single group 27 80Ah battery on a 27 footer. He had no idea his "computer" drew the current it did. Just a laptop right... ? His bank was cheap, dirty and replacing it every two years was reasonable to him, until it became an expensive lesson.

When I finally got called in his "new" battery was resting at 11.2V this after being "charged" two days ago by his alternator.... He was using WAY more power than he ever imagined he could on a 27 footer. His computer alone when charging and running through the small inverter was pulling 4.5 - 8A. His cabin lights he used to read by at night drew another 4A. His anchor light drew another 1A. His plotter, depth and tiller pilot another 3-4A. He also had cell phone chargers and a VHF... Did not seem like a lot but it was for the single G27 battery, and he simply could not keep up..

He spent upwards of $800.00 to be towed to a boat yard who porked him on a new battery, $180.00 for a replacement group 27..... (Sea Tow would have been a wise investment) So this lack of planning, and shooting from the hip, cost him nearly $1000.00 and in the end he still had an undersized bank.....

These types of cases are not just limited to sailors. I have power boat customers whom this happens to as well. I have one who fishes off shore who toasted his batts sixty miles out (massive Furuno system).. Lucky for him a good samaritan came along and got him started with one of their batteries. Bad for him is that neither his wife or kids are willing to do off shore fishing now. Something about 6' seas and everyone getting sea sick while the hand held VHF battery was slowly dying and not knowing if they'd be rescued....

You can still have an inexpensive bank, flooded batts fit this bill, but it does not rid one of the responsibility to size it for safety or to build a system with redundancies in it.. I love inexpensive flooded batts. Our entire bank cost us $210.00 and just ended its sixth season and will easily do a seventh and possibly 8th.. If I had the height to fit 6V's on our boat I'd easily expect I would get 10+ years.. The difference is our cheap bank was sized, installed and designed for longevity and has redundancy/safety built in.... A good design up front can be a cost saver in the long run..


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## blt2ski (May 5, 2005)

HERE is an electrical budget pdf sheet I found online at WM a bit ago. "It May" help one decide how big of a batter bank, charging system etc one needs. It does help on figure out how may amps per day/hr etc one uses, then you can figure out how big of a bank, charging system etc you will need.

Something like this will allow one to figure out if you can get away with a single size 24-31 battery as I use for my house bank. OR< if you need a bigger setup as mainsail has, showed in his last post why that client was not able to get away with a size 27, where as I am able to. BUT, if we discussed the power needs of my travel trailer I had.....I used two 6V batteries with the same foot print of a 27 12V, to get me as much or more juice as the 6V MS has, those would last me anywhere from 24 to 48 hrs depending upon how cold it was outside, with the furnace fan running. If my kids turned on the tv, they were drained in 4-6 hrs!

This link or equal links to battery usage charts, will help one decide on how big, many, style of batteries one needs. As one size does not fit all!

marty


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## sstuller (Nov 1, 2000)

This gives me a chance to tell a sea story. I spent a total of eight months in the Bahamas on three separate cruises. I never had more than two twelve volt Group 27 batteries - one for starting and the other for use as a house battery. My main charging source was a 50 watt solar panel. As long as I had a spare battery I knew I could start the diesel. No refrigeration of course. I relied on the local bars for cold refreshment and conversation. I was young (relatively) and foolish and had some of the best experiences of my life. Thanks. Steve S.


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## peterchech (Sep 2, 2011)

Maine I found this battery in Walmart for under $100, is this brand of decent quality in your opinion? It says distributed by Johnson, not really sure what that means...


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## hellosailor (Apr 11, 2006)

Peter-
"Maintenance free" is usually a dirty word. It means a wet lead battery, which will need to have the electrolyte topped up for best life, but with the cells conveniently sealed up so they can't spill and you can never add the electrolyte when needed.
It was a clever idea in the 70's but now, I think everyone would agree that either you want a battery that _can _be maintained (i.e. plain wet lead) or one that in theory never actually needs topping up (AGM or gel or Lithium, truly "sealed valve regulated").


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## peterchech (Sep 2, 2011)

hellosailor said:


> Peter-
> "Maintenance free" is usually a dirty word. It means a wet lead battery, which will need to have the electrolyte topped up for best life, but with the cells conveniently sealed up so they can't spill and you can never add the electrolyte when needed.
> It was a clever idea in the 70's but now, I think everyone would agree that either you want a battery that _can _be maintained (i.e. plain wet lead) or one that in theory never actually needs topping up (AGM or gel or Lithium, truly "sealed valve regulated").


I assumes the cells could be topped off by opening the caps on top, I didn't open them in the store but every lead acid battery I've bought had something similar to top off the electrolyte. But now that u mention it it does say maintenance free... Im confused...

I would love some agm batteries, but the only brand I find locally in auto shops etc is optima, which are known to be great batteries but just way overpriced, $4 per amp hour more or less... if anyone knows a good brand of agms and where to get them let me know, but shipping costs generally preclude internet ordering or else I'd have two trojan 6 volts and never worry about it again lol


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## hellosailor (Apr 11, 2006)

The "maintenance free" caps are often welded or otherwise secured down. There may be extra electrolyte, etc. to compensate a bit but the whole idea was "we can make it good enough so you never have to add water". Mainly for the crowd who find tire pressure and oil are also things too messy to do themselves.

Your local stores do carry falt-plate AGM batteries, from all the leading makers. They're almost impossible to spot even if they are on the shelf, but you can always as the clerk, or go right to the local battery distributor. Of course AGM isn't perfect either but that's a whole other debate. They'll be priced about halfway between the Optima and conentional wet lead.

Or of course you can stay with the MF battery and just make sure it needs replacement inside the warranty period. (G)


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