Low battery voltage can cause all kinds of weird things to happen. Some suggestions, pull the connectors on the battery and make sure they are clean and tight. The battery should be vented with no signs if corrosion under the seat. If it is more than 5 years old, I would go ahead and replace it. If the battery is dead/dying and you're not too far from a dealer, Mercedes will come out and jump the battery or replace it for free charging only for the battery.
http://www.mbusa.com/care/client-care/roadside-assistance.do
Good Luck, Dan