Keyless Transmitter Battery
WARNING: This page is about a different car, the 2002 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
To prevent static electricity damage to transmitter printed circuit board, touch steel area of housing with hand to discharge static electricity to discharge static electricity carries on body or clothes before disassembling transmitter.
See KEYLESS TRANSMITTER BATTERY under REMOVAL & INSTALLATION in POWER DOOR LOCKS & KEYLESS ENTRY SYSTEM - FORESTER article.