How do you replace key battery in a 2002 BMW 530i

SOURCE: 2002 BMW 325 - key locked in trunk

There are several suggestions out there on how to retrieve BMW keys from the trunk. Many of the ways I tried failed, and it takes 2 to 3 days to get a new key made up. In the coupe there is the center piece in the back seat that folds down. Then on the back wall there is material that will fold down that is held up with Velcro. Behind that you will find a rubber insulation that is mostly cut and looks like a door, but not all the way. Carefully cut the rubber to remove the piece. Now you will find a metal wall, but there is a large piece that is tack welded on. I got turned around and kicked it with the bottom of my foot and got 3 sides loose. Then a softball bat knocked the final side loose. Pull that out and trash it, the final barrier is the insulation that is held in place with plastic clips that can just be pushed down. After that you can a pretty large hole to work through and get the keys. Just put everything back in place other than the metal plate and you will never know anything was done.

SOURCE: 2002 bmw 530i key does not (remotely) unlock doors

Unlock vehicle. Enter vehicle. Close driver's door. Switch ignition ON and OFF. Remove ignition key. Press and hold unlock button. Press lock button briefly 3 times within 10 seconds keeping unlock button depressed. Release unlock button. Some models: LED flashes slowly for 10 seconds. Some models: Central locking system locks and unlocks rapidly to indicate correct programming. Repeat above procedure if central locking system does not work and LED does not flash or LED flashes continuously.