undervoltage
MB cars require a certain minimum battery voltage for all the electronics to function correctly. At some point if there is insufficient voltage, the car will not start even though you have headlights, etc. The error could be because the battery is weak or the alternator is not providing enough charging amperage to the battery. It could also be something more sophisticated with those issues as the symptoms.
Have your alternator and your battery checked by a competent MB mechanic -- indy or dealer as soon as possible.
Depending on the problem it could leave you stranded unexpectedly. That's the reason for the error message -- to warn you.
Good luck.



