Arrie

It was probably a sound of the short in the battery, which drained it right then.

I would get it replaced either by the dealer under warranty or on my own dime. Too risky to have it as it will do it again. It is not a question if but when.

Live Oak

I'm with you on this. While the car started normally this AM, I'm beginning to believe what we were hearing was battery water boiling. It seemed to come from the battery area of the car.

Every car I've had for at least the last 20 years has not allowed some thing, such as leaving a door open, to drain a battery --- the inside lights would turn off after a reasonably short time. Ditto for radio, which couldn't drain a battery overnight anyway.

The Mercedes tech's ruminations about "some thing" left on, or coming on in the middle of the night, that drained it, was not at all encouraging --- it had all the hallmarks of "reaching for reasonable explanation."

I'm going to get the battery changed. The question is, how will Mercedes respond to that? Will they replace it if it "tests" OK? Will they surmise that a complete failure without explanation is acceptable, leaving the owner with absolutely no faith in the vehicle (especially sending the wife shopping on a 97 degree day) and that they have no responsibility?

ttoE550

Dude, you've got a winning story: It's your only car. You can't possibly send your wife out alone with a battery that has most certainly failed once. If they can't find a power leak, then most certainly the battery needs to be replaced. If the SA won't do it, talk to the manager. Keep harping on how much you want your wife to be safe.

I'd stay away from the negative talk of "no faith" and challenging them with "responsibility." Understand that these guys deal with that talk all day, so they can tune it out. You want their help in keeping your wife safe.

Tjdehya

I am pretty sure that they are going to assume that it was user error and they wont replace the battery under warranty.
But if it happens again then you have a valid argument. Until then, you have no evidence that can to prove to them that you didn't leave the parking lights on.
But you can try, I doubt that they will call you a liar when you tell them that you know for a fact that you didn't.