A dead battery can be caused by a faulty seat control module that does not properly shut down. Spilling liquids on the front seats can cause these modules to fail.
Average mileage: 77,537 (65,000–94,113)
8 people reported this problem
Alarm goes off until it dies; first time car was jumped by Roadside Service and this worked for about 30 days; the battery drained a second time, but this time Roadside could not get anything more than the lights and doors to work; the steering is locked out; initial diagnosis was the ignition switch and a "dead battery", but then determined it was not the ignition switch or the "dead battery", but the passenger seat "and" the overhead console modules causing the drain. Both were replaced. This seems to be a common issue on the C Class itself for the 2001 thru 2004 modules. There is also a C320 forum on the same issue. MB USA does not think the problem extends beyond just a few vehicles.
Both modules malfunctioned soon after each other ..... simply left them unplugged. Apparently they cost $450 each .... cosmetic really if you don't need to move the seats .... if you do, plug them in, move and unplug