oufan2929

What do I need to do. I guess my lights stayed on overnight and the battery got weak and there's a feature on these cars that keeps enough juice in the battery to be able to start it, but all of the nav, radio, and such do not work. I charged the battery for a few hours w/no success. Do I need to just replace the battery? Or try charging it for a longer amount of time? Or maybe just disconnect and reconnect the battery? Thanks--Andy

Yacht Master

Andy try a search,

MB Road side service has been known to deliver and install MB batteries cheaper than going to the dealer.

IMHO once a battery has been dead, it never returns to it's original potential, no matter how much you recharge it. This is important because a weak battery makes the alternator work harder and allows for greater voltage swings and that spells death to the modules circuit boards, controllers, sensors, solenoids low voltage kills. Avoid the electrical gremlins get a new starter battery and check the SBC battery if it is older than 4 years.

X2Board

The battery for the accessories is not the same one that is used to start the car.

See this thread for details, and where not to go if you need a new one.

https://mbworld.org/forums/w211-amg/...w-battery.html

oufan2929

thanks guys

dyno

sorry, but that's simply wrong, whatever could be written in the other thread: when you are not in emergency mode it is the main battery (located in the trunk) the sole that is used for both starting AND for accessories.
The AUx battery located underhood is used for starting only in emergency mode after the battery control module detects that the main batt is low and therefore it cuts accessories.

X2Board

You are correct. I was told by a Mercedes tech that the primary function was SBC operation in an emergency and accessory power. After reading your post, I did my own research and found the attached document.


Thanks,
Marlon

wizos6

This is very true.. Infact sometimes the there is no problem with your battery and there is a serious draw coming from somewhere.
In my case the audio gateway is shot from the aftermarket stereo unit(at least that was what the dealer said) and also that they installed the valentine radar to the sunroof and that was causing a draw as well.
My car was stuck at the dealer for a whole week and they tested the front battery. 90% of the time it does not have to be replaced because as stated before its simply a backup for the SBC-brake system incase your other battery looses power.

Good luck as I know you will need it when it comes to electrical components on these cars.

dyno

I read that doc much time ago but I don't remember it was talking of the sbc thing.

weird that also my MB tech in Italy was saying the same thing about, ie sbc back up, but if you look at diagrams you'll find it is also untrue.

imho, the electric sbc is simply powered by the alt.

The AUX batt is normally dis-connected (except that once, at each ignition cycle it is being checked and, if necessary, charged).
When the module detects the main is low, first thing it disconnects accessories and in th emeantime it triggers the relais who connects the Aux battery in parallel. but this is not intended for powering a specific device. it just helps the electric system as a whole.
once the engine is started it will be the Alt's duty ..