Rear consumer battery dying overnight

[Sonnydas]

Hi everyone!

Car: 2005 SL500 75K miles.

Prerequistes: Excellent condition. Recently, 'Consumer' battery dies overnight. CTEK Mercedes charger only gets to 3 lights overnight. Battery is tested good and 1 year old. Front seats have sealed vacuum lines and DO NOT cause PSE pump to constantly run. No other leaks in PSE system.

Issue: Recently I changed a 5 year old starter battery with an OEM Benz battery. After changing I noticed perfect starting BUT rear consumer battery drained overnight. When connected to CTek charger overnight, indicator only gets to 3 orange lights. I've noticed recently after turning off car, keys out of ignition and complete shut down, I can hear a very faint fan running sound. Not sure if its in the command system head or climate control unit. Its very faint and seems to come from lower dash behind climate control. Everything else works perfectly in the car.

Question: Before starting to pull fuses to see which fuse causes fan sound to shut off, anyone experienced this issue? I've never used the bottom middle button on climate control (marked "REST"?) until I tried it for first time the other day and then issues began.

I've disconnected both batteries (REAR - FRONT) then reconnected (FRONT - REAR) after few hours and it didn't help.

Any guidance will be greatly appreciated!

 

[onefortheroad]

Rest should stop once car restarts tbh.

 

[LostKiwi]

We had a similar issue on our SL.
If we had been using Comand the battery would go flat overnight. I found if we turned off Comand and left the car 2 days, then used the car and recharged the rear battery but did not turn on Comand then it all behaved. If we then turned Comand on again we'd have to repeat the cycle of turning off and allowing the battery to go flat before the rear battery would return to normal.
I've since found that with the CD changer disconnected we can use Comand normally but haven't checked further as yet.

Our rear battery would fully charge on the CTEK though. It could be you just have a duff consumer battery.

 

[Sonnydas]

Does anyone know which fuses COMPLETELY kill 1) all components of Command system 2)All components of climate control panel and 3)REST pump. I will try pulling fuses today and see if the low fan sound stops.

The consumer battery is tested good. It is a 1 year old OEM. I will play with Command and post what I find. Thank you for the comments!

 

[Bay Leaf]

Am I doing the right thing by not locking my car when not in use in my secure garage. The reason I do this is to alleviate the alarm system, which to my way of thinking will save drain on the battery. My previous car a Jaguar, I was told to always lock it when not in use in the above situation as the on board systems don't shut down. Is this the case with MB. To be honest weather I locked the Jag or not it didn't seem to make any difference when it came to starting even if it had been stud for 4 or 5 days.

Your thoughts chaps.

 

[mioba]

I do the same thing with my w220. If I lock with key fob engaging alarm. The car is sluggish to start if left for a week.
So now I lock by pressing the lock button inside then lock the drivers door when leaving. Doing this doesn't engage the alarm. Car is locked in a garage and starts fine after 4 weeks.

If you think about it engaging the alarm keeps many things live, door sensors, tow away protection, internal sensors, computers etc - all using power.

 

[Bay Leaf]

Yes my thoughts too I used to have a Jaguar before this car and the general view on the forums was to always lock and immobilize as the electronic systems won't go to sleep otherwise. However I didn't bother apart from when going away on holiday but I never noticed any difference either way.

 

[Bay Leaf]

Now here's a turn up for the book. I got a six month warranty on the car with a well known company when I bought it, and it covers me for a new battery. So my battery being over seven years old and only showing 12.3 volts I made a claim for a new one and they paid out in full.