How do you deal with voltage balance when replacing one bad cell out of a whole battery? My understanding is that lithium ion battery cells need to be close to each other in voltage or else they suddenly rebalance when reconnected, and can burst into flames.
If you have just a slight imbalance it's taken care of by the BMS, as it continuously monitor and rebalances cells. That said, if you had used the battery for a while, and you need to change just one cell, you can't put a brand new one, it must be matched.
That's why we would recommend changing all cells. But the good thing is that changing all the cells in the battery will cost you perhaps $50 with our repairable battery. Compare that with $250-$500 with "classical models" where you need to buy a brand new battery