If you need one, spend the cash and get it! Repair the old one for another spare!

Split Fob case with box knife, cut approx. 1/16 or so deep)

carefully open casing (spring inside)

Remove circuit board

Order battery ($5-20)

Unsolder / Re-solder battery

put carefully together make sure flip key is working fine

place rubber bands around fob (not over buttons)

superglue

final product:
http://s1038.beta.photobucket.com/us...tml?sort=6&o=0

http://s1038.beta.photobucket.com/us...tml?sort=6&o=1

http://s1038.beta.photobucket.com/us...tml?sort=6&o=2