Folks, before you all declare the OP's battery is really dead, read here
http://f80.bimmerpost.com/forums/sho....php?t=1217987
A LifePO4 can disconnect itself for various reasons (mentioned in the docs in my thread), and to try to wake it, your LifePO4 charger must have a reset mode, read the manual. CTUK, Optimate and others support that mode.