Question: different size house batteries - SailNet Community
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post #1 of 3 Old 12-29-2017 Thread Starter
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Question: different size house batteries

Another battery question. Compac 27. 3 bank 15 amp smart charger (5A per battery). I have 18hp westerbeke, 50amp alternator. Grp 24 starter battery. Here is the rub, I have a Grp 24 and a Grp 27 deep cycle house batteries run in parallel. I read a post that stated it was ok to have different size as long as both deep cycle, others say no (both about a year old). Should I just suck it up and get two new Grp 24 batteries and do what I feel is the right thing? Will anything be damaged by the set up above?

Thanks for the input.
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post #2 of 3 Old 12-29-2017
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Re: Question: different size house batteries

I wouldn't go out and replace 2 batteries that were only a year or so old. You may have a shorter lifespan by having the different sizes but there's no reason to just run out and replace them unless your money is just burning a hole in your pocket. Whenever one of the batteries gives up the ghost, replace BOTH batteries at the same time with batteries of the same size and AH.
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Re: Question: different size house batteries

Batteries need to be identical and same age. if they are not the smaller one determines total AH rating X2 but this will also affect the life of the system as they charge a discharge at different rates. I would just suck it up and when they start to fail. buy them in pairs from the same source. I bought "deep cycle" batteries but in fact they are just heaver starting batteries. True deep cycle batteries have much thicker plates and are designed to allow a lower discharge and more recharge Cycles. where starting batteries allow for a higher discharge rate for a shorter time but not deep discharge.
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