Keyless Transmitter Battery
WARNING: This page is about a different car, the 2006 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
Remove the battery from the keyless transmitter.
NOTE:
Before disassembling the keyless transmitter, prevent damage by static electricity to the transmitter's printed circuit board by touching a steel piece of a building etc. with your hand to discharge any static from your body and clothes.