- Mercedes-Benz E-Class: Warning Lights
Important information to help you understand your Mercedes-Benz
Red battery message ( Visit workshop)
If you buy a battery that has been activated, it could be six months, or a year old, sitting in the warehouse, then the store's shelves until you bought it. You are giving away a fair sized chunk of it's lifespan, for the convenience of not having to pour a few ounces of liquid from one container into another.
So when car is dead/off the front battery is at 12.6 and the rear is at 5.4 (poor thing, lol. FYI it's a new battery, like 2 months old or 6 weeks)
When jumpstarted and running by itself, rear battery is up to 13.8 but the front is still at 12.6 and refuses to budge.
Red battery message is up.
My guess is it sounds like the front relay, right? What are thoughts on this?
The Best of Mercedes & AMG
So I fitted a new aux battery relay and it has solved the problem - no more red error message, yay!
My main battery got down to 2.2 volts after having sat for 4 days straight. It took a good 10 minutes just to get it to struggle n start and then it took a further 40 minutes to 'fully' charge the battery ie, get rid of the convenience functions message. Worth noting that unlike before, once the engine was running, the aux battery was now showing 14+ volts, wheras when I jump started it the other day and the main battery was showing 14+ volts, the aux battery didn't move from 12.6.
I've been driving it a fair bit this evening and the main battery is kinda at 12.2 or 12.3 volts, so perhaps the massive draining has compromised it's life a little bit, who knows. I'll give it a few days to monitor how it fares and then take it from there.
Bottom line - problem solved. Thank you MB World
So I fitted a new aux battery relay and it has solved the problem - no more red error message, yay!
My main battery got down to 2.2 volts after having sat for 4 days straight. It took a good 10 minutes just to get it to struggle n start and then it took a further 40 minutes to 'fully' charge the battery ie, get rid of the convenience functions message. Worth noting that unlike before, once the engine was running, the aux battery was now showing 14+ volts, wheras when I jump started it the other day and the main battery was showing 14+ volts, the aux battery didn't move from 12.6.
I've been driving it a fair bit this evening and the main battery is kinda at 12.2 or 12.3 volts, so perhaps the massive draining has compromised it's life a little bit, who knows. I'll give it a few days to monitor how it fares and then take it from there.
Bottom line - problem solved. Thank you MB World

Guess the cars are at the age that these parts are worn out with all the electronic modules on these cars. Never ran into this with acura/lexus/toy/honda.

I checked the battery voltage an hour ago and it was showing 12.7 or 12.9 so it's getting higher
I'll give it the benefit of the doubt for the next few days and monitor it's behaviour.As for the car on the whole, yeah, it's such a shame that it looks like with these cars, it'll be the electrical components that die out quicker than the core mechanics of the engine/tranny. It's a very fussy car, I must say. But....for that 5 minutes when it finally does work properly...it's one hell of an epic car with the power, looks and interior to match even some of the best that today has to offer. Long live W211 AMG.
I replaced the AUX battery, I replaced the CPS and the car still has same message. What should I try to replace next?
I replaced the AUX battery, I replaced the CPS and the car still has same message. What should I try to replace next?

So a couple months back I changed the aux battery relay and got rid of the red message etc and all was well. Then a few weeks after, my car died (electrically) again. Main battery had been drained stone dead to 3volts (this after driving it every day that week with no sign of battery power issues at all). Upon inspection, and a jump start, the car fires up, but the little battery doesn't show ~14v like the main battery does, it still shows 12.6 (lol it's been sat dormant for a few weeks now and it's still 12.6!!). I tried another aux battery relay, but when the car started, it still showed 12.6v, so I didn't bother running the car much longer as it's clear there is another fault.
Does this make sense to anybody? When the car is jumpstarted now, the main battery shows ~14v, but the little one shows 12.6 on my 'new' relay and on another one. HELP!

So a couple months back I changed the aux battery relay and got rid of the red message etc and all was well. Then a few weeks after, my car died (electrically) again. Main battery had been drained stone dead to 3volts (this after driving it every day that week with no sign of battery power issues at all). Upon inspection, and a jump start, the car fires up, but the little battery doesn't show ~14v like the main battery does, it still shows 12.6 (lol it's been sat dormant for a few weeks now and it's still 12.6!!). I tried another aux battery relay, but when the car started, it still showed 12.6v, so I didn't bother running the car much longer as it's clear there is another fault.
Does this make sense to anybody? When the car is jumpstarted now, the main battery shows ~14v, but the little one shows 12.6 on my 'new' relay and on another one. HELP!


The isolation relay is not always closed when the engine is running. 12.6 V is not that bad for the small battery when it is not charged.
Yeah the small battery seems good at 12.6v. Only problem is that it doesn't jump up to 14v like normal when the engine is running. Apparently the 'new' relay I tried has been tested and works fine, but I don't know how to check this with my voltmeter. I'm guessing I need to connect the pos and neg terminals to a battery and touch the voltmeter terminals on it, but doesn't this one need to be connected to the loom/ecu to operate, or...?
There are several stages for shutdown of consumer devices if the system and aux batteries are low in charge.
The normal voltage is 12.6V or above for the system battery. If it drops to 12.3V, it will show a warning some convenience consumer devices will be shutdown. If it drops to 10.4V, it shuts down the system battery, the aux battery takes over. There is a long list of items to check if there are warnings. The alternator, the system battery, the aux battery, the battery sensor, the relays and fuses.
The recommended procedure is to follow the DAS MB STAR which will invoke the WIS net to diagnose.
What I just seen are ad-hoc methods.
Wondering if it's just my main going bad or my aux; I'm thinking it's the main at this point...after jumping it 4 times in the past year. I had checked the aux battery disconnected and was getting readings all over the place; thinking maybe my multimeter battery needed changing.
Last edited by spinn; Oct 1, 2012 at 11:24 PM.









