On my Rushmore, I need to pull the keypad from the exterior wall, clean up the sealer, remove 2 small screws at the back of the keypad, replace the battery and then reglue the keypad using a two side gluing tape and then seal the top with clear sealant.
Givent the work required, use the best battery possible. I hear the battery will last 2 months average.
The dealer had to change it when we did our walk through back in March.
2012 Rushmore 34SB
2009 Silverado Duramax 2500HD