I probably would have been walking. Anyway, I'd go to Auto Zone or a place like that who will "supposedly" check with their equipment your charging system and the starting system for free in hopes of selling you something, a battery or starter or cable or anything. Your problem is narrowed down to a bad battery, a bad alternator, loose belt on the alternator, a bad starter or excessively low compression or possibly glow plugs, "IF" your fuel filters have been changed recently or if you know that the filters are not plugged or restricted. I could be wrong, but I don't think a bad starter would start a bad engine even if it had been charged for 24 hours at full force. And just remember that you can't drive a Mercedes "UNLESS" you have lots of cash or you are willing to get your hands dirty and risk maybe getting a knuckle busted every now and then, when the wrench slips because you had too much oil or grease on your hands as you were wrenching to replace that starter. Also remember that as soon as you say "it's a Mercedes"; the price automatically goes up. The same battery charge and process you just went through and you were driving an old Chevrolet, the mechanic would have charged you about $17.50 and if you said you were a college kid, it would have been even less. Also, remember SAFETY FIRST!

BenzDiesel