I had this problem when I first got delivery of my X (12/16) but the fobs were updated with new firmware, new batteries were put in and all was OK. The problem has re-appeared one year later on one of the two key fobs. I have replaced 3 batteries so far and each time the battery voltage drops from above 3V (full) to around 1V overnight. Both fobs are kept together and are far away from the garage. Can a key fob revert to an older version of firmware on its own?