My 2003 E320 had a battery malfunction warning come on red on the dash. I called the dealer and they stated that seeing the malfunction light was red and not yellow that one of the two batteries was bad. Mercedes Raodside came out and checked the batteries and said they had correct voltage on them. Seeing the car starts, the tech said he wasn't replacing the batteries cause thay showed good. He stated I need to take it to the shop so they can test it further. I will be taking it soon, but does that warning light also mean it could be the altenator? Sometimes the warning is not showing the malfunction, then I restart the car and it's on again. Could it be just a sensor sticking? Has anybody else had this problem?
Thanks!

 

Chances are that it is the small aux battery under the hood. There is the possiblity that the generator is faulty but most the time it is the small aux battery.

 

The aux battery only has 10.29 volts on it when I measured it. I've read that the warning will come on if it drops under 10 volts. You're prpbably right its just the aux battery. I've read that people open the battery and add water, but it's not made to open and I'll just buy a new one.
Thanks!