My wife's keyfob wasn't working so I figured I change the battery. Step one is to pry the clam shell apart.
And much to my surprise (NOT) the battery holder was suffering from the often reported bad solder connections.
OK, fire up the soldering iron.
There are three solder points to repair. The center one is surface mount, and the two outer ones have feed-through holes. Make sure to fully seat the battery holder down in them.
After repairing my wife's keyfob, I decided to check mine. Unbelievable lack of quality control on these things. While the electrical connection had not (yet) broken, the battery clip wasn't even level with the PCB. GM should really be ashamed of themselves for this part.