Q&A: Mixing Battery Sizes In One Bank

battery-sizes

Question: Due to space considerations I want to use  two 105 amp hour and two 150 amp hour batteries as a house battery bank. Would this arrangement be detrimental to the smaller batteries?

Answer: My gut reaction is that mixing two sizes of batteries would be a bad idea. Having said that, I really can’t think of a technical reason that it would not work. Let’s see what our battery guru, Justin at LifeLine Battery says:

It has previously been said that this is not a good idea; however, we have done some pretty extensive lab testing and we can find no differences in the batteries. Age is important but size is not. You can safely mix and match battery sizes in one bank.

Also, Sabre Yachts does this from the factory. This was one of the reasons we started testing this scenario. Sabre use a GPL-4DL and when they want to upgrade a battery bank they add a GPL-31T.”

So far Justin is batting 100% on everything he has told us about batteries, so I’m betting he is right about this too.

What I find interesting is that this is yet another incidence when what is taken for common wisdom about batteries and their use on sailboats turns out to be wrong. I’m guessing that there is more misinformation about batteries out there than just about any other piece of gear. I know that prior to working with Justin and writing the series of posts on batteries (see below) I, for one, was seriously ignorant on the subject despite thinking that I understood it. And I’m an electronics technician by trade who should, at least in theory, have a leg up on the run-of-the-mill boat owner.

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Meet the Author

John Harries

John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

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