if you've already tried to replace the battery's, make sure when you buy a used one or new that the fcc ID # is NOT the same as either of your fobs you have now, as they wont reprogram, thats why a lot ebay people show the back so you can check the part # and the fcc ID #.

the site you buy from should include instructions to reprogram the new fobs, or they can be found on line, or sometimes the dealer has to reprogram them due to years being different. not sure of your year for sure.