I have an old 2010 BMW X3. The unlock/lock buttons on the key fob stopped working, so I assumed it needed a new battery. But the key battery is sealed and the dealer wants $250/key. So with nothing to lose, I cut it open along the seal with a utility knife. De-soldered the dead battery, and soldered in these new ones. Used this super glue and the keys work great!
de-solder for battery replacement.