CLK55 AMG w209 with issues
Check the radiator fan runs when the car is warmed up and just stopped. Top up the coolant (use MB only not green or other generic versions or just demineralized water), it might be low from neglect or it might be getting used up quickly ie blown head gasket. Compression test would rule this in out. Leak down test would then find the source.
The heated seats can sometimes cause a fault and drain the power, check these. Otherwise not too sure if there are any other main culprits that are easy to check. Most of these problems you can go to a good independent mechanic, preferably who have worked on MB before and an auto sparky can track down battery depletion.







