Dead cell in battery

Build, Repair & Mod
1

I have a DIY 12S8P battery that I made about a year ago from salvaged Murata VTC6A 21700 cells which cost about 20% of new cells.

After 2 sessions in the weekend, my first cell string can no longer hold a charge, as shown below.

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When I plug in to charge it gets really hot because all the current is going to the low cell.

My question is should I try to replace that bad set of cells, or just be happy with the use I’ve had from it, and to play it safe and discard the whole thing? I don’t imagine trying to undo the nickel strip and plug in new cells will be easy, nor safe.

I think I know my answer but keen to hear any opinions.

2

Did you actually mesures the voltage of the dead cells?
Could be that you have a bad connect from that row causing the BMS to read wrong and put all current in it when charging.

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3

That seems like cell self discharge.
That can happen with old, reclaimed cells, and is more present in power cells vs energy cells.

It is more visible when the pack stays unused for a while, because the inbalance builds up and the bms can only work during end of charge.

I had a lot of issues with 30q cells in the past (100+ 16s10p packs)

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4

Does the answer align with this question - Do I want to spend time in the shop or out on the water? :wink:

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