Model S

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Key Fob Battery Keeps Discharging

I recently changed the battery in my wife's key fob and replaced the fob in the leather cover. I verified the battery had 3.27 volts before installing it. The next morning my wife was unable to use it to open the car. I checked the battery and found the voltage had dropped to just over 1 volt. I replaced it and the same thing happened but this time I didn't put it back in the leather cover. I think it may be that the fob itself is continually activating itself even when not in the vicinity of the car, thereby discharging the Batt. Has anyone else experienced this problem?


  • It sounds like the fob has become defective. If the car is in warranty, Tesla will replace it for free.
  • That is my thought too. I'm due to get in for the MCU thing next week so I'll ask them to check it and report back what I learn.
  • That’s weird because I thought those batteries had a very narrow voltage window, i.e. they worked at 3.2 V but were toast by 3.0. Not positive (no pun). Can’t imagine how it got to 1V without being shorted out or some other odd situation.
  • Before you replace the fob, leave it out of the leather cover for a while. maybe the cover is pressing one of the buttons.
  • I have been doing my annual replacement of coin Batts for all cars.

    Old batts were 2.95 to 3.0v. I understand they are considered good down to 2.7.

    Upon replacing the bat (2.99 v) in my spare MS key (New when I bought used car from Tesla 2.5 years ago, and never used) I could not lock or unlock the doors.

    Upon researching the problem, I found a possible solution for the OP.

    If the metal tab is bent at the back of the fob, it can short out the batt. Put a small piece of tape over it..
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