I’m usually on the W212 AMG forum however asking here for a friend with a newer C wagon.

She’s telling me that her key fob battery gets drained within a few days. And while she’s driving her car she can hear the tailgate motor intermittently working, although she doesn’t get a tailgate-open warning on her dashboard. It seems that is what may be causing her battery drain.

Thing is, I remember having a similar issue with my E wagon about 6-7 years ago. I’d hear the tailgate actuating, and sometimes I’d need to stop the car and click the tailgate closed just to be certain it wouldn’t open on me. But I cannot for the life of me remember what cured the issue, in terms of what I read and/or did.

Has anyone had a similar experience or happen to know what’s going on with the car?

 

Parasitic drain could be caused by key fob constantly pinging the car when it is parked. There might also be outstanding updates.

The motor mentioned might be the backup camera popping out when stopped.

 

The key should only consume power when responding to the radio transmission from the car when attempting to start or unlock it, or when pressing a button.
Does the spare key also have the same issue? If it does it could be a fault with the car module causing it to transmit all the time. If not then it’s going to be a fault with the key prob itself.

 

The key is also constantly sending signal for the keyless go feature to work so when you touch the handle the car responds. That said, modern MB keys should automatically go into standby when not moved. If the key is too close to the car, then the car keeps the key from going into standby which then also keeps the car from going into standby.