I have been search old threads with no clear answers. I was getting the consumer electronics turned off warning light. So I checked the battery and decided to put it on a charger. 3 amp over night. Came out and the bad battery light came on the charger.
I put a new battery in and two weeks later same warning light came on. Checked voltage on battery and it was 11.4. Running it was 13.6 which seemed little weak. So I replaced Alternator. Two weeks later the battery was dead again. Alternator still reads 13.5 to 13.8. Mechanic said that's fine. Took the battery back and said it was junk so they replaced it under warranty. Drove it for two more weeks, came out in morning and battery is completely dead. Jumped it, drove it for half hour warning light turns off. But in the a.m it reads low 11 v. Something is draining the battery. I know there is that battery control module back their. Is this the culprit? How can I test this BCM
Oh I did test the auxiliary battery and it's 12.6 at all times. Man im tired of this car. 21 years old, I know I know. 😮‍💨 Thanks in advance

 

It appears that there is a parasitic drain, but doesn't explain why the battery has charge for 2 weeks and then dies. I am dealing with something like this. I checked for parasitic drain and it is within specs <0.05 mA. But the battery loses 0.2mV overnight.

 

youall need a good CAN bus diagnostic system, like the one built into MB XDOS all else a great opportunity for the family to grab some meters and pay find the leak

 

well I'm going to try a used BCM from Ebay and see uf that works. Ive read some threads about. Then go from there

 

I was also searching for parasitic drain. Some things:

- Search on Youtube, there are quite some videos on this topic, especially for W211
- Seat control modules are a common culprit, you can test this by pulling out the fuses and checking the draw
- Alarm siren is a common issue, with age the onboard batteries will fail to hold charge. The alarm siren will keep requesting current from the car, preventing it from sleep and draining the battery
- Audio Gateway is a common issue
- Navigation unit can cause drain
- Voltage regulator can cause drain
- BCM can cause drain
- AUX battery can cause drain
- AUX battery relay can cause drain
- non-MB Original alternator can cause issues! There was a thread in W211 AMG section not too long ago if memory serves me right

I replaced my BCM (2005 CLS W219) with a BCM from a 2007 E-class W211. Also replaced the AUX relay, alarm siren, both batteries. I disconnected all Tele Aid/Phone capabilities and fiber looped out the components I dont need (you also need to code them out).

I can also highly recommend a bluetooth battery guard, it gives insight what is happening with the battery > https://mbworld.org/forums/c219/8443...ml#post8860681

 

Wow. This is crazy. OK thanks. If this ebay bcm doesn't work, I might just put her out to pasture. She is draining my wallet as much as much as the battery. 21 years old. This horse is tired.

 

Don't take a look in my build thread then hahaha > https://mbworld.org/forums/c219/8443...ld-thread.html

AMG = All Money Gone

 

How do you find time to drive that beast? Beautiful fire breather! Sounds incredible. I'll keep the garage warm for when you stop by and fix mine for me. 😬

 

My pitfall is working too much on the car and forgetting to drive and actually enjoy it

 

Thank you for the Bluetooth idea. I ordered one and installed it yesterday. Super helpful. Although, the one I bought, the Bluetooth range sucks.

 

Just an update. After enrolling in the MB engineering program I figured out how to remove the clip on the BCM. Put a different one in from Ebay and noticed that the connector had alot of corrosion on it.. cleaned it up and sprayed contact cleaner on it, and it works great now. No battery drain! Not sure if it was the corrosion on the clip or the bcm itself but for sixty bucks, my problem is solved. Can't complain. Thanks all!