I have a 00 CLK 430 that expereinced a drained battery. It was the original battery so I purchased a new one. The next day - dead. I took it to the shop (it's there right now) and they called to say everything checks out great (alternator, battery, no codes, etc.). Thoughts?

 

Lots of things can cause a battery drain.. Control units, SAMS, Navi, Phones..ect... A good tech will be able to find it. There are never fault codes for draws.