# lithium marine starting battery



## lithiummotobattery (Jan 2, 2022)

just joined to learn more about what sizes, power and cost factors involved in choosing a engine starter battery.
I've read a lot about lithium house batteries but very little about lithium starter batteries for marine engines.
Maybe there is an engine rep. on this forum....


----------



## boatpoker (Jul 21, 2008)

Switching only your starter to lithium may save you a couple of lbs. and a few inches but you now need a BMS and means of charging your LA or AGM batteries and lithiums at different rates from your alternator and your charger.
Too complex for me. I'm a KISS guy.


----------



## lithiummotobattery (Jan 2, 2022)

All would have to be switched to lithium, correct.


----------



## johnsonjay17 (Jul 20, 2015)

lithiummotobattery said:


> just joined to learn more about what sizes, power and cost factors involved in choosing a engine starter battery.
> I've read a lot about lithium house batteries but very little about lithium starter batteries for marine engines.
> Maybe there is an engine rep. on this forum....


Because Lead-Acid is the superior choice for a starter battery. Lead-acids are suited for rapid discharge and rapid charge, are best suited for staying fully charged. All the things you need in a starter battery and all the areas that a LI battery perform poorly in. 
LI batteries are superior for house batteries. A house battery needs to be able to deeply discharge, able to handle many partial charges, stay at partial charge with no damage. This are the things that a Lead-acid do not do well.

JJ


----------



## StarTracker (Dec 26, 2021)

Look at LTO. That's my next move for start battery. a 6SxP build will keep your maximum charge rates and low voltage cut offs outside the range the cells can tolerate. Some are running them without BMS. Manufacturers say they are good for 20-30k cycles, don't mind freezing temps either. I will test it to confirm at some point, but I believe because of the acceptable voltage range of the LTO, that they may be able to act as the buffer battery like a lead acid start to protect the alt if a Lifepo4 house bank's BMS slams open.


----------



## colemj (Jul 10, 2003)

One can always just forgo the start battery and use the LFP house battery for that purpose.

Mark


----------



## overbored (Oct 8, 2010)

A friend has a race boat with a 1GM10 diesel and uses a rechargeable LI jump start battery to start the engine. weighs about 5 lbs. been working fine for about 5 years. he has no house bank


----------



## StarTracker (Dec 26, 2021)

colemj said:


> One can always just forgo the start battery and use the LFP house battery for that purpose.
> 
> Mark


Depending on your alternator and BMS. That's why I am warming to the idea of LTO as the emergency/start batt. Gives me a failsafe solution if the BMS decides to trigger a cut off.


----------



## boatpoker (Jul 21, 2008)

1.2lb, lithium booster pack, $100 on Amazon, will start my 55hp Westerbeke 7 times


----------



## lithiummotobattery (Jan 2, 2022)

For those with a diesel engine, The LiFEpo4 would be a superior choice. Unless, you actually NEED the extra 50 + lbs
of ballast. Same goes for the house batteries. Lets hear from those that DID make the switch...


----------



## StarTracker (Dec 26, 2021)

lithiummotobattery said:


> For those with a diesel engine, The LiFEpo4 would be a superior choice. Unless, you actually NEED the extra 50 + lbs
> of ballast. Same goes for the house batteries. Lets hear from those that DID make the switch...


I'm starting to think you're an advertiser. Looking for engine reps, first post on the product and saying it is superior. Maybe I'm wrong. But LTO gets my vote for start batteries going forward, eliminates the lead acid for start to protect the alternator or various systems to shut down alternator before BMS disconnects fully avoiding high voltage dumps and blown diodes.
Lifepo4 for house battery, absolutely! $/usable watt they win hands down these days weight, charge acceptance etc are all bonuses. I'm going plastic prismatic, Winston/Thundersky if I can afford it for the cold benefits. I don't like the aluminium cased ones but that's because of my boat not the cells themselves. Big powerboat I'd probably go with those. Bank will be sized for 1/2 my desired bank size, paralleled after the BMS. This gives me redundancy.
Usually run the whole bank, but a single BMS or cell failure won't eliminate my house bank only reduce it. 

Lithium booster pack(usually made up of 18650 lithium cells not lifepo4). Excellent. I have two. Love them. One of my most used tool and totally handy for testing pumps and systems in a pinch.
Lifepo4 start battery? Nah. Not gonna sell me on that one. Although maybe start battery is a misnomer. I usually configure so the lithium house bank can be used for cranking, the start battery is more an emergency start and protection for the system from a hard disconnect by the BMS. LTO is looking much better for that than lifepo4, and with the massive amp delivery rates, many times higher than Lifepo4, I can go to a small battery. It looks to me like a 26AH 6S1P build will crank my engine just fine and weigh next to nothing.


----------



## boatpoker (Jul 21, 2008)

1 - alternator, 1- charger, 1- G27 start battery, 4 - 6VDC golf cart house batteries and 1- G31 thruster/windlass battery.
Cheap, replaceable anywhere, simple, most reliable and almost idiot proof. I'll stay with what I've got. I see no benefit to the complexity and expense of installing a lithium system in my application.


----------



## colemj (Jul 10, 2003)

StarTracker said:


> I don't like the aluminium cased ones but that's because of my boat not the cells themselves. Big powerboat I'd probably go with those.


How do sailboats and powerboats differ such that one should have plastic case cells and the other aluminum case?

Mark


----------



## StarTracker (Dec 26, 2021)

colemj said:


> How do sailboats and powerboats differ such that one should have plastic case cells and the other aluminum case?
> 
> Mark


There are exceptions, like this battery you can see on Maine Sail's site: IMG_1940.jpg
aluminium cells make sense in here. They conduct heat, the whole thing is engineered and extremely heavy duty bus bars are used reducing any movement variation between cells. Pricey bit of kit though. 

In a big powerboat I'll likely have lots of room in a nice dry location to work with, probably even decent head room. You get more amps, they require less compression of the bank and they are cheaper. I will have room to build a properly waterproof box, with cells well secured, built well above the bilge with lots of extra padding, can build in dialectric sheets that won't chafe much between the batteries, and easily monitor for signs of corrosion and water by building the box oversize, even building the cells up on a framework inside the waterproof box so water never gets to the metal.
I can't see that on many sailboats unless you do what I'm doing and mounting them in some very premium storage space under the settee. Even so I still won't be using the metal ones if I can avoid it.

On top of that, while some powerboats can go way out there, I don't see many that do. Never know what someone will do with a sailboat though. 

Maybe I'm just old fashioned, but conductive and easily corroded boxes holding that kinda power give me the heebie-jeebies anywhere, I can get over my discomfort by building well enough to live with it in a decent sized powerboat. I can't see a way to sleep well at night with most sailboats spaces.

With the cycle life possible I can see a battery bank lasting 20 years in some cases or more. Do I trust that the owner after the next owner will be as paranoid as me about keeping that aluminium clean and dry? 

I can easily imagine someone working in a cramped space on a sailboat in the event of an emergency letting a cable or tool touch the top of the battery accidentally, how many of us have the ingrained understanding that the ground is safe and to be careful with the hot? The inverse is true in these. I do not in any way consider the plastic wrap to be enough. A little chafe and you're off on an adventure. Plastic cells have thicker skins, often with ribs to create air gaps for cooling, and therefore give you a bigger margin before they chafe through. No matter happens what the skin isn't conducting electricity. While not ideal, a bit of water getting to the base of the batteries won't change anything. With the aluminium cells...
Imagine the following for example, you have a steel boat. You build the bank in the bilge without it's own watertight enclosure, as I would have to if I wasn't relocating it. You get a build up of water around the bottoms of the cells, and any tiny pinhole or chafe in the cheap shrink wrap. 

"I am so glad I watched the Big Battery Tour and heard them talk about the positive terminal being connected to the outside of aluminum case batteries. Clamping these batteries together without the insulation between them is a recipe for disaster. In my opinion, as in your post, this extra step should always be part of the conversation every time clamping aluminum cased batteries together is discussed. I'm taking my batteries apart to add the insulation material right away."


https://diysolarforum.com/threads/insulation-material-between-aluminum-case-cells.15388/


----------



## colemj (Jul 10, 2003)

Have you built a LFP battery? 

Only a minority of the metal case shells have their case connected to the positive. Most of them are the opposite. Those types of cases are made specifically to go into OEM products with insulated spacers or cases, proper containment, ventilation, etc. There is nothing worrisome about them as long as they are put into service properly. This is definitely possible on any boat.

Your concerns about water seems to be only about these being installed in bilges and engine rooms. And without appropriate containment/protection. Many boats wouldn't have those restrictions - particularly given the small size and weight of LFP.

Your concerns about dropping tools across the terminals...well...come on. This is a hazard regardless of batteries, and one shouldn't work on batteries of any type unless they understand the precautions necessary. One shouldn't also touch a screwdriver to your AC feed, but many people are perfectly safe with their 120/240V supply panel at home, and their distribution panel on the boat.

Chafe should not be an issue regardless of case type. That is an installation error, not an operational one. It would take a sawzall to chew through a plastic case - any case movement that could do so would be snapping connector bars and distorting everything before it chafed. A cramped space is a perfect place for these batteries. No need to build an alter, guild it, and walk around it for LFP. Pretty much hook it up properly and ignore it.

Mark


----------



## boatpoker (Jul 21, 2008)

We no longer do many deliveries but if we are interested, among the questions we ask is ... Are there any lithium batteries fitted ?

If the answer is yes, we refuse the job.

This may seem over the top for some and I've no doubt you guys are better than this but as surveyors we have been horrified by the amateur lithium installations we have seen. I won't bore you with the many examples we have but this is one of my favourites ....
Two aluminum boxes full of lithium cells with no ID as to what lithium chemistry they contained or how many cells were in there and no access for inspection, all connected directly to an AGM battery, all charged by an internally regulated alternator and a 40amp charger set for LA batteries. Zoom in and look at the battery cable connections wrapped in white duct tape and lying against the aluminum battery case. Also, owner claimed he had a BMS ... it was a voltmeter !

There were also 8 connections on one battery terminal and some pretty shoddy connections everywhere else. Next season we will be refusing surveys with lithium installations unless we know the installer.
We may be a little cynical but what we see on a routine basis has made us that way.


----------



## StarTracker (Dec 26, 2021)

colemj said:


> Have you built a LFP battery?
> 
> Only a minority of the metal case shells have their case connected to the positive. Most of them are the opposite. Those types of cases are made specifically to go into OEM products with insulated spacers or cases, proper containment, ventilation, etc. There is nothing worrisome about them as long as they are put into service properly. This is definitely possible on any boat.
> 
> ...


Yes, the worst were for a couple e bike builds using 18650s 13S10P about 14 years ago, why?
None of the plastic ones have positive cases. I like none more than some for products where people, often with the best of intentions are DIY'ing something they might not fully understand. I wish there was more info in the 2020 NTSB report, they mention 42 incidents caused by lithium batteries in the US, I would like to see more details, I suspect mostly related to devices with less safe chemistry being charged, but that's only a theory.

Most boats? I would say some boats, particularly powerboats.
Not across the posts, but between the ground post and the case. Lithium banks last a long time, do I want to bet that every single technician and owner in the next decade or two are conscientious about this potential risk that isn't shared with any other battery I'm aware of at this time? 
Yes a saw for the plastic ones. But for the shrink wrap on the metal ones, not so much, even a sharp wood edge or a bit of grit will do the job.

That is precisely my point, in an OEM product like the picture I linked I think they are good, better than the plastic in fact. But that's a well designed product and as you said yourself proper containment etc. Or at least one that won't end up in the news like this: Lithium batteries withdrawn following boating fires in France - The International Institute of Marine Surveying (IIMS)

In the last 6 weeks I've seen two builds that were downright alarming with aluminium ones. Is that the owner's fault for how they installed them, and we can't blame the battery? Yup. Would it have bothered me as much if they were plastic? No. I don't know yet what the failure rate is.

Can the aluminium ones work? Sure. Would I pick them over the plastic ones for my sailboat at today's prices? Absolutely not. If they were half the price of plastic? Maybe, I'd have to think about it, definitely not for anyone else though. I guess I'm a big sissy, and I'm ok with it. Whether it was my fault or not, at the end of the day if something I installed, even if it was installed in a way that met the applicable standards and someone got hurt because of it, I don't think I could live with myself. 
I went back and ground out a perfectly good repair from a decade earlier and redid it free of charge, because I was losing sleep over it. Nothing was wrong with it, despite the ridiculous stunts the owner pulled with the boat, not even a spider crack. As I learned more, I realized I didn't have the minimum safety margin that I felt was acceptable later. 

At the end of the day, it's just my opinion and it's worth what you paid for it.  I'm quite happy being wrong, but what I'm seeing in the field gives me pause with the metal cased ones. I am itching to get my hands on a set of LTO cells though. In everything except price they look like a holy grail product. Ultra long cycle life, discharge and charge rates far beyond anything any current boats need and the cherry on top is that in 6S configuration with only a low voltage cut off I can't see any way to screw them up, making them a viable drop in substitute for the lead acid start battery. I've even read about someone who ran them to 0.0V and charged them up without any major ill effects. Only the hope that they'll drop in price by the time I'm done my refit stops me.


----------



## Michael Bailey (Sep 10, 2021)

lithiummotobattery said:


> just joined to learn more about what sizes, power and cost factors involved in choosing a engine starter battery.
> I've read a lot about lithium house batteries but very little about lithium starter batteries for marine engines.
> Maybe there is an engine rep. on this forum....


What you decide to do depends on what kind of boat you have, how you use it, how much do want to spend on batteries and how much you want to think about batteries. I am old school. So is my boat. Lead acid batteries work well and don't cost too much. We have a modern charger that's always in service at the dock. We don't use much battery power when we are on board. I kept the last set of batteries for 8 years and only replaced them because they were old. I didn't want to wait for them to fail. I do keep an eye on the dc volt meter to know how its charging. Nothing fancy here


----------



## colemj (Jul 10, 2003)

@StarTracker You have conflated LFP with LiPo, which are completely different chemistries and safety profiles. This is a disservice to people attempting to learn about LFP. Those batteries in France that were banned were LiPo power packs, which don't have any place on a boat as a main power source. They were not the LFP chemistry commonly used in boats. Your fears are also mostly grounded in LiPo issues. You won't find these fire problems, etc with LFP, as they simply do not catch fire.

Again, it is a minority of the aluminum case brands that have the case tied to the positive. The others are tied to negative, and there is no issue of grounded tools touching the case.

The drawback for LTO is the size and capacity. Lithium is denser energy in smaller dimensions than LA, while LTO is the opposite. The faster recharge rate is meaningless because few boats can provide that much charging.

Mark


----------



## colemj (Jul 10, 2003)

boatpoker said:


> I won't bore you with the many examples we have but this is one of my favourites ....


I've seen all of that and worse, many times, on LA installations. Both are equally dangerous.

Mark


----------



## StarTracker (Dec 26, 2021)

colemj said:


> @StarTracker You have conflated LFP with LiPo, which are completely different chemistries and safety profiles. This is a disservice to people attempting to learn about LFP. Those batteries in France that were banned were LiPo power packs, which don't have any place on a boat as a main power source. They were not the LFP chemistry commonly used in boats. Your fears are also mostly grounded in LiPo issues. You won't find these fire problems, etc with LFP, as they simply do not catch fire.
> 
> Again, it is a minority of the aluminum case brands that have the case tied to the positive. The others are tied to negative, and there is no issue of grounded tools touching the case.
> 
> ...


Let's look at it another way. What do you like better about metal over plastic cased batteries for DIY build/install, not talking about engineered batteries where I already agree they're better? 


No. I understand exactly the differences between them just fine thanks. That's why I said: house bank lifepo4, jump pack li-poly, start I'm undecided as of yet. I have built all but LTO so far. I was using the news article as an example, you will note I specifically referenced the fact that I wish NTSB would differentiate by chemistry. I have a suspicion given the installations I've been seeing with them that we will see fires and other issues caused by them. lifepo4 won't internally light off but improperly installed will absolutely cause fires. Big battery cables make excellent light bulbs with enough amps applied, lifepo4 is good at delivering a lot more amps in a hurry. My concern with them, and it's concern not fear is that they introduce one more way someone can create problems, and based on history when they can, they often will. 

I don't care if it's a majority or a minority. The bad things many, many boat owners manage to do with batteries mean I am strongly in favour of anything that reduces the risks. Metal cases do not reduce the risks. As I said before excellent for engineered batteries such as the Lithionics, better than plastic case in that use. A positive case means way more chance of an issue, yes it's only some. But that means it is some. Some is not 0. Negative cases mean that a positive cable touching the top of the battery, can also cause issues. I can't tell you how many times I've found batteries with cables lying loose on top. Should people do this? No. Do I think they some will do this even with a metal battery? You bet. 
Do I think they should be banned? Not really, but just because you can use them doesn't mean you should. Regulations are often blunt instruments. The risk of regulation simply saying none of that lithium stuff if you want insurance are real. I want a lifepo4 house bank, so this concerns me. Badly installed LFP especially in metal cases increase the chances of this happening, and frankly I'd be amazed if they even go as far as differentiating by chemistry, I think reports like the NTSB one or the one about the French stop-sale that do not call out the specific chemistry increase that risk. Enough incidents and they can solve it by simply saying lithium batteries mean not insurable, which I am very interested in not happening. 

2. LTO vs FLA vs Lifepo4. 
Not true, sorry. While I think it will be some time before there's enough data to be sure, I see the potential in LTO for start. Not for house. House is at least for now better off lifepo4. Lifepo4 also didn't start out where it is today, it was an evolution and price change as competition happened that led it to being as good as it is now.

The following is from Wikipedia, not my favourite source of info but good enough for a first look. There are more variables that suggest LTO will be an excellent start battery but this post is already getting too long so: In order the numbers are: energy density by mass(Wh/KG), energy density by volume(Wh/L), specific power or power to weight ratio(W/KG), self discharge rate(%)
Lead acid: 30-40, 60-75, 180, 3-20%
Lifepo4: 90-160, 333, 200-1200, 4.5%
LTO: 60-110, 177, *3000-5100*, 2-5%

Faster recharge rates are not meaningless, nor discharge rates. In big banks like house it doesn't matter. But the emergency/start bank does not need to be a big bank, utter reliability and long life are more valuable to me than cost/Ah. It does 5 things that I think are interesting for a start bank. I don't think it's ready for prime time yet, but I think it will continue to evolve and is already at the point where it is viable. 

1.Prevent issues from the BMS opening the circuit on the lifepo4, same as the FLA start would do without adding complexity of control systems to go all Lifepo4.
2. Function regardless of temperature meaning the bank can be mounted in a cockpit locker or other small out of the way space.
3. Provide much higher charge/discharge rates allowing you to reduce the size and weight of the start bank and leaving more of both for the house. 
4. discharge to 0.0 without failure, albeit with a potential reduction in total capacity. I like things that can fail safe. 
5. Charges quickly, a smaller bank can still accept what my system can deliver. 

Let's take a Prismatic LTO 20AH cell for example. It can charge at 3C(60A) discharge at 8C(160A) continuous or 25C pulse for 30 seconds without damage(500A)
a 6S1P 20AH battery will give me plenty of juice for an emergency start, it charges at what my alternator can deliver flat out, and a bit less than my shore power charger can deliver(80A). In theory I don't need a BMS in 6S, only if I went to 5S. This means I can recharge it in 20 minutes from dead flat. 
Compare that to an equivalent lifepo4. I picked Topband simply because it was the same supplier and only 5AH/cell more than the LTO. 
a 4S1P battery will charge at 1C(25A) discharge at 3c(75A) pulse discharge of 5c for 10 seconds without damage(125A).
To get close to the same charge/discharge and start rates, I would need to go to 4S2P, add a BMS, and control system to shut down alt before BMS opens at the top end. That would give me 50A/150A/250A respectively.


----------



## boatpoker (Jul 21, 2008)

colemj said:


> I've seen all of that and worse, many times, on LA installations. Both are equally dangerous.
> 
> Mark


As have I but they are a helluva lot simpler and cheaper to fix.


----------



## captrockcod (Jan 9, 2022)

johnsonjay17 said:


> Because Lead-Acid is the superior choice for a starter battery. Lead-acids are suited for rapid discharge and rapid charge, are best suited for staying fully charged. All the things you need in a starter battery and all the areas that a LI battery perform poorly in.
> LI batteries are superior for house batteries. A house battery needs to be able to deeply discharge, able to handle many partial charges, stay at partial charge with no damage. This are the things that a Lead-acid do not do well.
> 
> JJ


I wouldnt say lead acid is superior for a starter battery (they have been the only choice) or that they are suited for a rapid discharge, while also suggesting that Lithium are not.
Lithium will way out last a Lead acid, be much smaller, and not let you down when you need it the most.
A simple DC to DC charger is all that is needed. Renogy makes them in 20 amp and 40 amp.
You can get some very small Lithium batteries that can handle a huge starting current.


----------



## johnsonjay17 (Jul 20, 2015)

captrockcod said:


> I wouldnt say lead acid is superior for a starter battery (they have been the only choice) or that they are suited for a rapid discharge, while also suggesting that Lithium are not.
> Lithium will way out last a Lead acid, be much smaller, and not let you down when you need it the most.
> A simple DC to DC charger is all that is needed. Renogy makes them in 20 amp and 40 amp.
> You can get some very small Lithium batteries that can handle a huge starting current.


Let's discuss chemistry. The only Lithium battery I would allow on my boat is a LiFePo4. The LiFePo4 typically see a drastically shortened life with any discharge beyond 1C. So for a typical 100AH that means you start to damage the battery at anything beyond 100 amps. That is why batteries designed to last for a decade have a BMS that shuts off the battery at anything over 200 amps on a 100 AH battery. (The exact amperage may differ based on the manufacturer). I know they produce LiFePo4 cranking batteries. I have only a few experiences with them and they lasted about 4 years. That is less than a properly cared for AGM. I know the few folks I have worked with to install them did it mostly out of wanting to have the most expensive thing thinking that meant it was the best. I don't see a LiFePo4 cranking battery solving a problem it just spends money. Of course I learn more every day point me to a long lasting LiFePo4 and let's compare cost vs life.
I have not seen a small LiFePo4 that will out crank a lead acid. Those that I have seen are Li-Ion and as I stated above I would not allow one of those on my boat. Li-Ion is much more volatile than LeFePo4 that is good if you want a small powerful package. That is really bad 100 miles offshore and it melts down.
Of course the amount of cranking amps is part of this equation we haven't talked about. I am assuming 500-600 amps if you are only starting a very small diesel that uses less than 100 amps that would change things.
I also want to state that the technology is changing and I am purposely a slow adopter. I want the safety proven in the wild by many early adopters before I install in my boat or one of my friends.

Thanks,
JJ
PS the LiFePo4 cranking battery I took apart used the same Prismatic cells as the house batteries. Those cells will not last at 6-8C discharge.


----------



## StarTracker (Dec 26, 2021)

johnsonjay17 said:


> Let's discuss chemistry. The only Lithium battery I would allow on my boat is a LiFePo4. The LiFePo4 typically see a drastically shortened life with any discharge beyond 1C. So for a typical 100AH that means you start to damage the battery at anything beyond 100 amps. That is why batteries designed to last for a decade have a BMS that shuts off the battery at anything over 200 amps on a 100 AH battery. (The exact amperage may differ based on the manufacturer). I know they produce LiFePo4 cranking batteries. I have only a few experiences with them and they lasted about 4 years. That is less than a properly cared for AGM. I know the few folks I have worked with to install them did it mostly out of wanting to have the most expensive thing thinking that meant it was the best. I don't see a LiFePo4 cranking battery solving a problem it just spends money. Of course I learn more every day point me to a long lasting LiFePo4 and let's compare cost vs life.
> I have not seen a small LiFePo4 that will out crank a lead acid. Those that I have seen are Li-Ion and as I stated above I would not allow one of those on my boat. Li-Ion is much more volatile than LeFePo4 that is good if you want a small powerful package. That is really bad 100 miles offshore and it melts down.
> Of course the amount of cranking amps is part of this equation we haven't talked about. I am assuming 500-600 amps if you are only starting a very small diesel that uses less than 100 amps that would change things.
> I also want to state that the technology is changing and I am purposely a slow adopter. I want the safety proven in the wild by many early adopters before I install in my boat or one of my friends.
> ...


I am of the same opinion re: Lifepo4 as start. Negates many of it's benefits. Love them for a house bank, and a house bank of suitable size for me(320-400AH) the issue is moot, because even 1C is 4x more than my starter is specced at, 20% higher than my maximum shore power charger as well. Lead acid or hopefully LTO soon for the start.


----------



## jlodolce (Feb 25, 2008)

I have been studying switching to LFP for 2 months. I had to answer for myself the same questions as the discussion starter had. Perhaps you already have answers.

While some LFP manufacturers advertise LFP starter batteries, AGMs are better starter batteries, because they have greater surge power than LFP to start an engine and are much less expensive. You can do away with your starter battery and just use you house LFP bank, but I like having an isolated starter in case the house bank gets depleted. AGM starter batteries are inexpensive, so why risk it?

Your dockside charger can isolate the LFP house from the AGM starter. You have to add a 12-12 DC-DC isolator/regulator to your alternator system to charge the AGM starter and LFP house batteries simultaneously. I will use a Victron Orion 30A model for about $300. You can get a 15A model for $200. The alternator current goes directly into the AGM starter battery, then to the isolator/regulator which then controls the current going into the LFP house bank.

Below is a good link to a Great Lakes Cruisers Community 90 minute seminar I attended virtually 2 days ago. Well worth watching. Covers all aspects of switching to LFP

MX00102-g: Lithium Battery Technology_1


----------

