Well I got a new car a while back, and the key fob stopped working a month in to having it. I figured the battery died. Started using the 2nd fob for a bit, until it stopped working also within less than a month. Decided to change the battery, when I went to do so, I noticed the battery clip had come loose. I put it back in place, and it worked! But, it continues to come loose from the constant banging I apparently put it through.
Here comes the soldering iron.
The key fob opened relatively easily by the seams (just used my finger nails and heaved) and it opened. The battery clip looks like it had some form of paste holding it in place before, but that has broken.
The best method to do this seemed to be to remove the battery and clip, apply some solder on the key fab PCB where the old solder/compound had been holding the clip on, then I'd put the clip back on over top of the new solder, and melt it with the iron and push the clip into the melted solder.
Done, i put the battery back in, closed 'er up, tested and it worked.
Now this is much better! It doesn't come lose when I shake it around =)