I replaced the battery and it was dead one day later??

You must have an ignition-off draw. That means that when the car is shut down, there's current flowing through one or more circuits in excess of what's allowable and in your case it's draining the battery. The first thing I look for is for example, the trunk light or glove box light remaining on. In your case, if you had a fully-charged battery go dead in one night, the draw must be considerable. With the ignition and all accessories off (and the underhood light disabled), you could disconnect the negative battery terminal and use a 12 volt testlight across the cable end and the negative terminal. If you see the bulb light, I'd say that's enough current to drain your battery. Pull fuses one by one until you find which circuit is at fault when the light goes out. That's a good place to start. If you want to find an MBZ specialist, here's our directory link for you: https://repairpal.com/mercedes-benz-repair-in-bartow-florida