Continuing the autopsy. The busbar. The BMS was slightly damaged.
Did you understand what went wrong in the first place? In my experience trying to weld too thixk nickel with strong welds create internal damage to the cells, and very high self discharge after thermal cycles of the cells.
I have no doubt that everything is exactly as you describe, but I think the underlying cause in this case is different. In each pair of two batteries, one is completely discharged and the other is not, and the voltage readings are the same in all four pairs. If self-discharge were the cause, I don’t think the readings would be the same.
However, I am not a expert and could be wrong.
By the way, what are the welding recommendations in this case?
If this photo is what we’re talking about, it’s a busbar made up of 6 layers of 0.15mm tape. The elements were welded together using two 0.2mm thick layers.
Without any hope, I took one cell from a disassembled battery (P42B) with a voltage of 0.7 volts and tried charging it. First, as a Pb battery to 2.4 V at 0.3 A, then as a Li-Ion battery to 3.7 V at 1.5 A. I expected a lot of heating and a high internal resistance. However, the cell charged and was slightly warm by the end of the charge. Internal resistance measurements with a YR 1035+ showed 6 mOhm, which is typical for these cells. I’m surprised. I’ll leave it for a few days and monitor the self-discharge.
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If you are lucky, its just the bms billing the cells, but with 6 stacked layers of nickel, heat damage to the cell during welds is possible.