I just experienced the same problem with a used gen 2 I purchased yesterday and the fix is as follows. The battery has drained so low that it isn't recognized by the charger, so the battery needs to be "jump started" so to speak. The same goes for many batteries in devices and even auto's and motorcycles. So, with the charger plugged into the wall, carefully plug-in & unplug multiple times until it responds and begins to charge. What this does is gives the battery a small "jolt" each time until it can be sensed by the charger. It took my device approximately 15-20 times, so be patient. Good luck bro.