Need advice on adding 4 new cells to 32 older cells

Hey guys, I’m trying to rebuild a 12s4p 30Q battery. This is my first time taking apart a battery and I’m coming in hot with questions. :slight_smile: I’ve taken apart the prebuilt battery back and have 32 good cells measured at 4.17V, as well as 16 bad cells. I’m going to scrap the bad cells/make use of them with microcontrollers or something.

So with the 32 good cells I was thinking since I already have the proper 12S BMS, I can add just 4 new 30Q cells to make a 12s3p?

Also, my other worry is that since my current cells are charged to 4.17V each, if I buy new cells and they come uncharged at ~3.7V, would I need to charge them first to 4.17V? Or is it safe to install with the old 4.17V cells and charge everything up to the same 4.17V before using it. I think I may be describing the job of the BMS?

Those are my questions and I appreciate any help!

No.

Your only decent options here are to use those to make a 10S3P, a 16S2P, an 8S4P, or to scrap 6 of them and make a 12S2P.

Under narrow circumstances you could scrap 6 of them and add 12 new ones to make a 12S3P but every single P-pack MUST contain the same number of old and new cells unless you want terrible results.

You absolutely cannot add 4 new cells and make a 12S3P, it won’t work that way. The battery will have horrible sag, become unbalanced, and destroy itself if discharged very far down.

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Damn, alright. Thanks for the response!

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Yep everything Brian said is correct, unfortunately batteries don’t work that way

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