Expert: John Kingery - 8/30/2010

Question
Hi, i just read a response concerning the bmw 5251, 2001. i
have one car key that has not been used in years and it now
does not work to open the door and the trunk remotely, nor
doe it work while trying to lock the car as well. i  
understand from reading your response to a question that the
battery in this remote charges once used. can i still use
this key and get it to work for the door and trunk functions
after I start using it in the ignition while driving?

Answer
I don't recall answering the prior question, and am not aware that BMW used keys with batteries that charged themselves while driving.  This may be the case, but I am not aware of it.

Most BMW key remotes have a replaceable battery, and then need to go through a sequence to be synchronized with car.

Your owners manual should cover the details.