Hi I have a w211 2003 E500 I am having a problem with the battery constantly getting discharged. So, here is what I have done so far:

New battery in the rear, new battery under the hood.

I have disconnected both seat modules and overnight same problem.

Then I started going through the system a little more and realized there was a 1.2amp drain from fuse 006 in the trunk. Audio Gateway I think so I removed that fuse and still the same problem.
Next day I removed fuse 24 and 26 cd changer and radio. Same problem.

It happens overnight 10-12 hours and the car won’t even unlock with the key. Any ideas??

 

My 2003 E500 had the battery control module in the trunk by the spare tire fail killing the battery every night. Just throw $100 bills at it and you can solve it.


battery control module part # 211-540-69-45. It's a part connected to the battery (main) in the trunk.

 

My 2005 E320 CDI has been to 2 different dealers I think 9 times now for these same symptoms over the past 6+ years. It's damaged 2 batteries and is annoyingly intermittent, which makes finding the root cause so tough. The battery control module was replaced a couple years ago; still had problems after that.

Having technicians poking around has caused its own share of problems. After one trip to the dealer, my COMAND unit would turn on by itself even though the car was turned off, locked, and sitting in my garage. That one was a loose ground wire.

As near as I've been able to figure out, it's related to a third-party bluetooth puck. Leaving the puck connected seems to be the one thing in common with finding a dead battery the next day. It's unplugged now and fingers crossed, I haven't had any battery issues in the past 8 months.

 

I had this happen off and on for a couple of years. I thought it was the cell phone in the center arm rest, so I replaced the battery in that and I thought that was it. The problem came back steadily for a couple of months. I brought it to the dealer and they could not figure it out so I put a quick disconnect on the battery and would open it every night so the battery would not discharge.

I had to bring the car to the dealership to get the airconditioning system reset and told them about my problem. Finally they were able to locate the problem. It was the teleaid system and they needed to shut it off without disconnecting it. If the disconnected it I would have the SRS warning light on the whole time, they worked with MB and were able to disable it and that fixed the battery draw.

I had gone thru every fuse in the car several times and the reason I could not find it I believe is that the teleaid system does not have a fuse (or at least one you can access) because it is a safety system.

Recently several mornings I have gotten in my car to a low battery but the car starts every time. This has to do with the phone/audio system. I get the error message about consumer electricals being disabled but there is enough juice to start the car. When I unplug the phone from the cradle I have never had the problem. The phone goes into a weird state sometimes and will not work properly without tacking it out and re inserting it. When I see this happening I just take it out for the evening and so far no additional problem.

The one clue about the teleaid system being the culprit was every so often the teleaid system would try to make a call and as you know it is an analog phone and not able to make calls.

I hope this may give you a hint to solve your issue.

 

Follow up to my November post (#4). It wasn't the puck. The drain recently killed a year-old battery and then in 3 weeks killed another one. I now have new batteries front and rear, so we'll see what happens.

Curious to hear about Tele-Aid being the problem daddcap. I was wondering about mine. I had it upgraded to MBrace some years ago. Several months back, I was annoyed with the MBrace app never able to find the car location or unlock the doors. I called Tele-Aid/MBrace to have them send the unlock code. It never worked. Spent some time in the car talking to MBrace tech support and their judgment was the system wasn't synched with MBrace properly as communications weren't getting through. I was told to have the dealer resynch MBrace. So, that's on my dealer to-do list (along with fixing the blasted trunk lid wires. Their fix lasted 3 months. My 4 repairs lasted over a year each. I'm just tired of doing it).

 

If anyone is looking for the BCM, there's a much better price on the part than in the link above. HuskerParts seems to have the best price from a dealer: www.huskerparts.com Take a look at the electical control diagrams and such. It appears to be $386.10, if I have the right part. You can also call them to confirm for your year and model. It appears to have been superceded by an updated module.