YouTube is awesome. I had a bad lithium battery for my Ryobi tools. I had dropped it and it wouldn’t take a charge. I almost threw it away and decided to take it apart and see if I could see anything wrong. It looked ok but wouldn’t take a charge. Then I found a similar video for lithium’s. After watching I learned to check each cell and I found one low one causing the fault. The vid said to use a 9v to do the same jump on the low cell. That did revive my battery.