I had a small rectangular object on the bottom of the case too (didnt open the case, it opened by itself after a jump:). Soldered it back and the esc works again. 5 batteries after that and counting. :)
The case opened today again, so i glued it. Im glad as long as the esc works.
Offtopic:
http://www.youtube.com/watch?v=sG18bAN_HHA Took a little video, damn camera didnt like bumps tho. :(