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Forum Index : Solar : Different Vintage Batteries in Parallel

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InPhase

Senior Member

Joined: 15/12/2020
Location: United States
Posts: 178

Posted: 03:07am 04 May 2021

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I'm sticking with flooded GC2 type 6 volt golf cart batteries. I understand them and know how to keep them alive for years and they are readily available. So increasing capacity means adding batteries in parallel at a given voltage.

I can't afford to buy, say, 16 batteries all at once. What are the pitfalls of putting batteries in parallel that are months or years newer than the existing? If it can be done at all, what special precautions need to be addressed?

Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 04:43am 04 May 2021

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In parallel probably not too many problems with lead acid that I am aware of.

Lithium, I would never do it. I have had three lithium cells fail dead short circuit, and with cells in parallel, a failure like that would be doubly expensive, and possibly dangerous.

Cheers, �Tony.

mab1
Senior Member

Joined: 10/02/2015
Location: United Kingdom
Posts: 209

Posted: 02:42pm 04 May 2021

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Should be ok. Older batteries tend to have a slightly lower rest- voltage so if there's a big difference in age the new batteries tend to discharge first/slightly more than the old ones, then when charging, the old batteries fully charge first. If the new and old batteries are connected together for an extended period without charging the new batteries will gradually lose charge by trying to maintain the older batteries at above their rest-voltage.

As long as your batteries get fully equalised and/or have a reasonable amount of float charging time they'll be fine as the new batteries will have time to fully charge & equalise. If your batteries don't get properly charged and equalised for an extended period then the newer batteries will tend to fall behind the old ones.

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