Keyless remotes are standard features on most BMW vehicles, including the E36. These remotes, whether they are used to control the door locks, boot release, remote starter or panic alarm, can be used for a long time by maintaining them with a working battery. You can change the battery in your key fob in a matter of seconds.
Pry the top cover of the remote from the bottom with a flathead screwdriver, needle-nose pliers or another flat object. This may require some leverage but should be done as gently as possible. You may have to work the flat object around the edges of the remote or find a small indented spot.
Notice which direction the battery is turned and which side is facing up.
Lift the small latch holding the battery in place and gently remove the battery from the remote.
Place your new battery in the same spot and position as the old battery and replace the latch over the battery.
Snap the covers back together on the top and bottom to return the remote to its proper position.