Well i was riding and i busted my stator cover and it set for about a month. then i got a new one and put it on and my battery was almost completely dead. i got it on charge now....maybe the stator grounded out all the juice while it set?
Maybe it wasn't fully charged when you brought it home? Anything is possible, but it doesn't matter now. If it still won't hold a charge after you fixed it then troubleshoot it, but no need to try to divine why it lost a charge after the fact.