36V 5Ah Battery

This is a replacement batter for both bikes. Maybe 'someone' took the battery off and left it charging in a hotel room. Maybe 'someone' left it on the top of the car and drove off.  

More likely, your kid wants to ride 24/7 and just wants a fresh charge all the time. Make dreams come true, parents. After all, it wasn't YOU who left it charging in the hotel room.