My grandson played on the mower after I parked it and left the key in it. next day the key was in the run (no headlights) position. I tried to start it and nothing. Yes, I checked the battery... 12.8V. But it acts completely dead; I did try hooking up the battery charger (It immediately goes to FLO (Charged). no headlights, the hours meter does not even come on... I checked all connections, everything looks good.