I believe the key only needs a few hours to re-charge.

Does eveything else work like when you hit the remote the lights inside come on inside? Then the X is receiving a signal but only lock/unlock doesn't work. Does the central lock button on the console work?

If all those are true then, it might be your general module. Read this thread:

http://www.xoutpost.com/x5-e53-forum/...ry-change.html

Good luck!