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!


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.


Damn, alright. Thanks for the response!


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