both remote keys stopped working

Hi Guys,

I have not found anything similar using the search, maybe one of you can help. We have a 2006 X3. My FOB stopped working about a week ago but the key of my wife was still working fine. So I started to get ready replacing my battery following the instructions here on the board. However, now my wife's remote lock/unlock also stopped working yesterday. I highly doubt that both key batteries died at the same time.
One possible failure I think might the charging of the keys while driving? Has anyone seen that befoe.

Any other suggestions are very welcome, I am out of warranty s obviously I would like to do some research myself before having the dealer look at it.


Thanks so much

Markus