This is my own fault

[KNS]

The key batteries for '04 BMW are charged every time you have the key inserted in the ignition. Amazingly, eleven years later, both keys are still working fine.

[GH85Carrera]

I have carried the very same car keys for 20 years. I still can't find the dang battery. Where does it go?

[MBAtarga]

Originally Posted by KNS

The key batteries for '04 BMW are charged every time you have the key inserted in the ignition. Amazingly, eleven years later, both keys are still working fine.

Not so on my 2011 3 series I bought used in November. The "spare" key apparently was never used as it was a 1 driver car. Twice my wife has gone to use the key and it won't even unlock the door. And these have the internal non-replaceable battery.