tvs92000

this information always appears on cluster of w211 E240. the main battery runs out quickly after a night. I checked the charging to battery, it is ok, but I could not find any reason that the main battery runs out quickly, even it is new battery. Someone can tell me why?

vettdvr

Battery relay in trunk? Did you check for current drain after the timers go out to see if you are drawing too much current with everything shut down.

tvs92000

Do you think that this fault appeared due to BCM(battery control module)?
I switch off all consumer and key off car, the battery voltage drop about 0,23V after 2hours. When I connected the das to car and saw that the discharge value was about 8A, it is so much, so after 1 night the battery is exhausted and can't not start the car. Someone has any good idea to help me

forcefed4door

Well until you get it figured out just remove negative terminal on battery when parking for awhile. Atleast you won't have a dead battary everyday.

vettdvr

Voltage isn't the key here amperage is. What you must do to confirm current draw is have an ampmeter that will measure about 10 amps. Put it in series correctly connected to the Neg. terminal of the batter, Close the trunk wait about 15 min then check for current draw. If you have .075 amps or so you are ok but my guess is you are 2 to 3 amps which will kill the battery. Disconnecting the neg terminal will work to prevent it going dead over night. Check my post about being stuck away from home.

tvs92000

Thank you for good comment. I would to ask you 2 things:
1st- How can we measure amps if we close the trunk?where can I have to measure
2nd- we suppose that the measured amp is about 2 or 3 amp, what can we do next? which part is faulty? I checked and see that all electrical consumers are switched off after removinf key from car/

vettdvr

You will need an ampmeter good for about 10 amps two long wires with clips.

Remove the negative battery cable and do not connect this cable to the battery.

Connect the two leads from the ampmeter one to the neg cable on the battery and one to the neg cable that is not connected. Make sure you have the polarity correct on the ampmeter to prevend damage to the meter.

Some meters have a diode to protect them and I dont know what you are using.

Then close the trunk on the wires to the ampmeter with the meter outside the trunk, wait about 15 min and then read the meter. If you have more than my guess .05 amps you have a problem. The reason you use a 10 amp meter is you can pull 3 to 5 amps before the timers time out.

Other option would be go get in trunk lock yourself in and use flashlight to read the meter, but I would NOT recommend that.

tvs92000

I have perfomed as you say, and recognised that the amp is about 3,1-3,9 A. that is so big problem. temperary I have found nothing.

vettdvr

You HAVE found a problem, If the amps are greater than 1 that's way too much with it all powered off. You can pull the fuse to the power seat memorn and the overhead panel and see if this drops the current draw. If not, I still suspect the BCM in the trunk connected to the battery is defective. Your choice now is to take it to a dealer to have it confirmed the BCM is defective. I replaced mine and found there is a mechanical relay internally that can fail causing the malfunction.

I wish you the best on your choice of resolution.

rogerbotswana

Hi All. Similar problem. Bought new front battery, new rear battery and new alternator. turns out that water got into the bcm somehow at some stage [kids i presume]. contacts were slightly corroded, and used some contact cleaner about 9 usd. Alternator and batteries cost around 800 us. expensive lesson. check the bcm and use a decent electronic contact cleaner before spending huge cash on something quite simple.