Thought I had a dead battery and really didn't want to spend another $200+ for a new one. Turns out the battery was fine, just had a low charge that the charging cradle deemed insufficient or unrecognizable. This took less than 10 minutes to do, and now my "dead" battery is charged back up for full capacity! I used a Greenworks battery but this technique should work for any lithium ion battery where you have a good one and a "dead" one. Never use a source greater than the voltage of the dead battery you are trying to charge and I am not responsible for any damage or injury you cause from trying to use my technique.