I've have two packs get badly unbalanced this year, In each case, one row would hit the 3,0LVC when the rest of the cells were close to 4.0 volts. My theory included (a) faulty BMS (non balance) that was leaking down that row of cells or (b) running the battery well past the C-rating of the cells. In one pack. I had run 13A per cell thru some 21700's only rated for about 5A, In the other, it was a steady 6A per cell on generic 18650's.
In both cases, I replaced the BMS with a balance BMS and was able to use the bike packs, I noticed that the unbalanced row on both backs would hit about 4.0V on charging, but never got that extra .2V to match the other cells. Also noted that my capacity was down. Eventually, I replaced the rows on both batteries with new cells. This was hard work, by the way, and required me to buy a spot welder,
The mystery continued with my purchase of a Littokala cell tester. It can discharge up to four cells at a time cell to LVC, fill it back up, and tell you how many maH were used and the final voltage, I expected to test the cells and find at least one from eacb row that had diminished capacity. I did not. All tested to the rated capacity marked on the cells, or even higher, and reached a charge of 4.2V The explanation is that the Littokala discharges at 250ma or 500ma for its load test. So it isn't comparable to the 2A-4A per cell often seen on an ebike,
I conclude that put of the 70 cells in the above two batteries, at leas two of them are unable to recharge or sustain current at their rated C-rates, but I'll need a better tester to find them,
