I have had a little luck charging one cell at a time in a 2s pack to bring it back. What I did was use a male fan plug from a computer and it fit in the balance plug and you start at the red wire and the first black and that is one cell and so on through all the cells. Need to charge as a 1s pack. I do that till I get each a little above 3v and then start to charge as a regular 2s