So starting a few months ago I had begun to experience frequent battery issues with my car. I would leave the car for 2-3 days and it would be unable to turnover, sometimes I would even leave it for 1 day and I would need to use a jump starter. But after a few days it would need to be completely jumped.

I took my car over to mercedes to see if there was an alternator issue, problems with the battery, or drains. They said everything was okay, but I had a 100mA drain which really wasn't anything to worry about if I am driving it every day.

They recharged my battery fully for me and I was good to go. It worked fine for about a week, but then the re-occurring issue began to start up again.

As a result I decided to do some experimenting. I charged the battery myself, by hooking it up to a battery charger that plugs into the wall, as well as installed a negative disconnect. Fully charged the car and used an ometer to check how much the battery was being drained and it fluctuated between 1.5amps and 3 amps. Next what I did was flip the negative disconnect and left it for a day, reconnected it and plugged it into the charger and the battery took about 1/2Amp charge for a few minutes, nothing really. Then I left it connected for a day, came back and it took around 3-5 amps for an hour or so.

Few things to note, after the car would die and I would have to either use the booster or jump it I would get an abs warning message as well as an esp warning message. Those would go away after a little while. Also, this only happened a few times, but I would come out and I would notice the car would be tilting to its back right, and when I would start it would say warning airmatic low, and then it would pump right back up.

I've heard a few theories on it, one of them being that the car is continually running its diagnostic tests, and because they are not finishing they keep restarting and draining the battery... not sure if that is true, but it could explain the fluctation in the ometer.

 

I have a 03 S class that is doing the exact same thing. What i found out is that when i turn the car off and lock the doors the battery would lose ampage, so what i did was after i cut the car off i left the doors unlock and to my suprise, my battery didn't lose any amps and was fully charged as it should be,even after sitting for a few days. In my situation, the cars factory anti theft system was somehow pulling current when it was activated after the car was off.