# Installing Dual Batteries and dual battery switch



## TSOJOURNER (Dec 16, 1999)

I am installing a dual battery system and switch in my sail boat and I have a single marine charger that charges my single battery now, so if I install dual batteries with a dual switch, in order to charge both batteries at the same time with a single battery charger with the battery switch in off position do I need to use a dual battery isolator and hook it up with the alternator lead at the isolator in order to charge both at the same time. Maybe some one knows of a web site that has a diagram Thanks lmddmc


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## btrayfors (Aug 25, 2006)

It would help to know a bit more about your boat: it's size, type of use, and battery charging capabilities.

I assume by "dual batteries" you mean two batteries for the house bank, and by "dual switch" you mean a common 1-2-Both-Off switch.

The preferred way to wire multiple batteries these days is to combine all house batteries into a single bank, rather than treating them as separate banks. There are several reasons for this, among them the more efficient charging potential and less wear and tear on the batteries.

The idea is that you wire all house batteries together, as a single bank. Next, you wire ALL onboard charging sources (battery charger, engine alternator, wind generator, solar panels, etc.) to the house bank, through appropriate circuit protection devices and regulating devices.

Now, you have one large house bank which is charged by a variety of sources...whatever you have available.

Then, if you have a separate starting battery, you use a device like the Xantrex EchoCharge or the Balmar DuoCharge to keep the starting battery charged. These devices are not "isolators" and they are not "combiners". Rather, they are smart switching devices which sense the voltage level on the house battery bank. Whenever that voltage exceeds about 12.8, they will recognize that something is charging the house batteries -- it doesn't matter what -- and they will bleed off a bit of current to charge the starting battery.

This works great in practice, since starting batteries typically require very little charging to keep them topped off. However, the house batteries require a lot of charging, which is why you wire all onboard charging devices to them.

Hope this helps.

Bill


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## TSOJOURNER (Dec 16, 1999)

I have a 25 'Catalina I am just installing a total of 2 batteries one for starting and one for lights the boat came with a marine single battery charger. When I am at the marina I want to hard wire that charger to both batteries dual battery switch is off and shorline connected,correct me if I am wrong, I will then need to use a battery isolator to charge both batteries , when I am using engine charging system I can just run the dual switch in the all mode


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## sailingdog (Mar 19, 2006)

The preferred way to do this is to use either an echo charger or a battery combiner, with the echo charger being preferred to the combiner for a few reasons-as mentioned by Btrayfors.*

Using isolators is generally not a great idea, as they cause a voltage drop that a less sophisticated battery charger, probably much like the one you have, can not compensate for, leading to the batteries not being properly charged*.

Running with the switch in the BOTH position is not ideal, as that can often lead to both banks being dead if you've forgotten to change the position back when the engine is not running. Also, it can lead to a dead alternator if your crew accidentally turns the switch through the off position while the engine is running.

BTW, I'd highly recommend you read the *POST* in my signature to help you get the most out of your time here. It has tips on searching sailnet, writing a good post, posting photos, etc..

Welcome to the asylum.



lmddmc said:


> I am installing a dual battery system and switch in my sail boat and I have a single marine charger that charges my single battery now, so if I install dual batteries with a dual switch, in order to charge both batteries at the same time with a single battery charger with the battery switch in off position do I need to use a dual battery isolator and hook it up with the alternator lead at the isolator in order to charge both at the same time. Maybe some one knows of a web site that has a diagram Thanks lmddmc


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## timebandit (Sep 18, 2002)

Why not just run the hot charger wire to the same post on the switch as the engine charging wire then charging will be the same all the time.



lmddmc said:


> I have a 25 'Catalina I am just installing a total of 2 batteries one for starting and one for lights the boat came with a marine single battery charger. When I am at the marina I want to hard wire that charger to both batteries dual battery switch is off and shorline connected,correct me if I am wrong, I will then need to use a battery isolator to charge both batteries , when I am using engine charging system I can just run the dual switch in the all mode


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## sailingdog (Mar 19, 2006)

Doing that means that you would have to turn the battery switch to the "BOTH" position for it to charge the house and starting battery banks. This is generally something to be avoided, especially when dealing with an AC powered charger that may be left running unattended for long periods of time.


timebandit said:


> Why not just run the hot charger wire to the same post on the switch as the engine charging wire then charging will be the same all the time.


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## timebandit (Sep 18, 2002)

What would be the difference between my way and charging a house bank made up of a group of batteries wired together and used as one?? 

I hate electricty--I can't see it and it can kill me--fast


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## ckgreenman (Aug 22, 2008)

Just buy a dual bank charger and sell the single charger. I bought my Marineco 6 amp dual bank charger for about $120 at Bass Pro Shops.

Edit: 
Sorry. It was a Promariner not a Marineco.


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## SEMIJim (Jun 9, 2007)

ckgreenman said:


> Just buy a dual bank charger and sell the single charger. I bought my Marineco 6 amp dual bank charger for about $120 at Bass Pro Shops.


For the same money he could keep his current single-channel charger and go with this: Blue Sea Systems e-Series Battery Switch Dual Circuit Plus [tm]










plus Xantrex Echo-Charge










The switch would connect starter battery to starter, house (bank) battery (or batteries) to everything else, and allow both to be charged from alternator or single-channel charger, "independently." None of that "1/2/BOTH/OFF" nonsense, having to keep track of which battery you charged last time you were motoring, etc.

That's the solution I was going to upgrade to this season, before the economy forced us to belay all non-critical repairs or improvements.

Jim


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## TSOJOURNER (Dec 16, 1999)

Thanks everybody for your help I think I have the picture now. Semijim idea with the xantrex is what I am going to do Mark


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