Removal Procedure

Insert a small coin between the 2 halves of the transmitter case at the slot provided near the key ring hole.
Twist the coin in order to open the case.
Open the transmitter case.

Fig 1: Opening Transmitter Case
Courtesy of GENERAL MOTORS CORP.
Slide the battery out of the bracket to remove (2).

Fig 2: Removing Battery From Transmitter
Courtesy of GENERAL MOTORS CORP.