- Mercedes-Benz E-Class: Warning Lights
Important information to help you understand your Mercedes-Benz
Red battery message ( Visit workshop)

If you do the work yourself, it is prudent to disconnect the positive side of the main battery before working on the smaller one. The main battery backfeeds the smaller one and unless you are extremely careful you can easily ground the small battery positive connection causing a direct short and possibly expensive repairs. There is a step by step method posted by vettdvr (sp) that will keep you straight. Battery Warranties are about as consistant as the weather. I would expect the dealer to dodge but who knows, it is worth a try.
I got about 6.5 years out of the factory battery(s) but it is a low option car in a mild climate.
your profile does not show any location so it is hard to help you with locations, but I have confidence you will find a battery.
your profile does not show any location so it is hard to help you with locations, but I have confidence you will find a battery.
Last edited by sdifox; Jan 4, 2010 at 09:10 PM.
Last edited by sdifox; Jan 6, 2010 at 07:56 AM.
The Best of Mercedes & AMG

Should I replace the Aux Battery ? Or is it more than that ?
Should I replace the Aux Battery ? Or is it more than that ?
.If you had the load on the battery with then engine off and after a while started you might get a low battery warning from the main battery if the main battery was old and losing reserve capacity.
Steering hard. wow,, it is hydraulic and not electrical so no electrical reason for this but hydraulic problem.
Red Check Alternator,, possibly very low main battery putting too much drain on alternator where the voltage drops excessively triggering the alarm. Or alternator failing from having to continually boost battery from pulling power while engine off.
or just failing.Pass park light.

My suggestion given all the issues you have listed is take it to the dealer to do a detail check.
You need some data.
What is the voltage of the aux batt engine off.
What is the voltage of the main batt engine off,, then on.
Is the alternator charging?
These are just the beginning of problem solving.
How old is the main and aux battery?
So to answer your question on replacing the aux battery given the info you have listed is.
Here's a pdf I found on the web, detailing functions of each battery - a little hard to comprehend thou
W211 Two Battery Vehicles Function.pdf
this one on removal of AC cover
w211065 Auxiliary Battery R&R.pdf
here's whats happening with my car:
Aux Batt: 12.48 V (Orig Made in Italy one)
Main Batt: 11.7 V (black battery) this is the culprit then
From NTB I'm getting one for $188 with 7 yrs warranty - Can someone give aH rating for OEM battery, just to make sure its the right one
here's whats happening with my car:
Aux Batt: 12.48 V (Orig Made in Italy one)
Main Batt: 11.7 V (black battery) this is the culprit then
From NTB I'm getting one for $188 with 7 yrs warranty - Can someone give aH rating for OEM battery, just to make sure its the right one
Check on ebay for a replacement cover.
Make sure it is AGM correct ahr rating and vented properly outside.
You are right 11.7 V main is probably a dead cell in the battery assuming the voltage comes up with engine running.
- Aux Batt: I got from Walmart Everstart Maxx EH14BS - $65
- Main Batt: I got from Advance Autoparts: $99.98 w/ 2 yrs replacement warranty, it was $132 w/ 3 yrs warranty but I might not keep the car that long (its a 12v 850CCS 95aH)
Stealership prices were:
Aux: $188
Main: $306 w/ tax
I started getting the red battery warning about a week ago. Checked the main battery voltage at 12.4 and alternator output at 14.2 v idle. Put chargers on both the front and back as we don't drive the car for long distances. Initially, warning disappeared and every thing goes back to normal. After a few days off, start the car and red warning is back. Very disappointing. I begin researching BCM problems etc. I decided to check the aux battery with leads off and got 10.4V

Moral: You cannot trust these Chinese batteries. I asked for and was granted an adjustment but was warned that no further warranty would apply. I asked about the manufacturer. Answer "Somewhere in China".
So if you get stranded by a battery problem and you don't know where to turn, just face east and scream for somewhere in China.
Next time, I am going to be very inquizitive about what I am buying.
No price for peace of mind.. Enjoyin the car everyday! If you picked it up you might have noticed how VERY heavy the battery is. When I tried to remove mine from the holder I thought it was still bolted in.
My wife was laughing because it wasn't. Guess I am getting a bit older and really noticed the heavy weight of the battery.





