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.Google+
Car Problem Reports
Mercedes-Benz C240 Dead Battery Due to Failed Seat Control Module
Mercedes-Benz C240 Problem
Average Mileage: 101,582 mi (70,000 mi - 155,400 mi)
Replaced my battery in my 01 c240 mb, after that I have experience no haz flashers, no turn signals, no wipers,trunk release doesn't work and fuel gauge doesn't work. Oh yeah my rear sun visor doesn't go up or down. Has anyone experience these problems before, if so what was the cause.
Visitor, 2002 Mercedes-Benz C240, 70,000 mi
Passenger seat is causing a drain on the battery resulting in a dead battery every 24 hours. Also have a short in the steering column which further drains battery. No fix yet but it would be helpful if MB would just admit they have a problem and share the solutions rather than sticking their head in the sand and claiming their car must be perfect because it is after all a MB!
Visitor, 2001 Mercedes-Benz C240, 87,220 mi
Battery drain..all of a sudden. Had vehicle recovery comp(roadside assistance) out a number of times( all happened over xmas) jump started car ok, would take it for a run to charge, but drain woould re-appear within a couple of days. Loaned battery charger from friend..removed battery to re-charge, however, his charger was faulty and s no luck. Called vehicle recovery company as I needed another jump start..they arrived and re-connected the battery. Car turned over, but by now..the removal of the battery, and possibly low power had now blown the rear SAM as once the battery was re-connected nothing worked, i.e. indicators, hazzards, wipers, washers, mirrors, boot release, petrol gauge, etc. Only thing that worked were the headlamps, heater, and radio..So SAM replaced(!) £390!. This did not cure the drain..re-occured 2 days after picking up from the repair shop. So, was told that it was a faulty battery, replaced the battery ..cost£70. Guess what, no joy..the problem returned around 3 days later, completly draing the new battery. Car just returned to me from the repair shop at a cost of £523!!! The problem..now resolved...WAS a faulty seat control!
Visitor, 2002 Mercedes-Benz C240, 95,000 mi
After several battery replacements and costly failed diagnosis, found heated seat module defective. Of course after the warranty expired.
Same problem… I have my fuse pulled for the module and stored in my console for quick re insulation.
Visitor, 2002 Mercedes-Benz C240, 120,000 mi
Same thing, dead battery, SRS error on computer it is the seat control unit.
Visitor, 2002 Mercedes-Benz C240, 73,000 mi
This happened to me . They wanted $1400 to repair. This is very expensive and was told that this was a large problem in the 2002 C class. I feel like Mercedes should correct the problemas this is just making their pockets fat.
After many jumps and several trips to repair shop finally figured out it was this overly priced seat module. Horrible design for this to be a possibility. My MB must be a lemon as it's had several of the common problems reported on this forum. For a pricey car, horrible design and reliability. No more MB for me.
Visitor, 2002 Mercedes-Benz C240, 110,000 mi
Same problems as stated above. Battery was dying and found out the cause to be the passenger seat module. Have the seat module unplugged as a fix to the drain for now.
Visitor, 2001 Mercedes-Benz C240, 107,033 mi
Battery continually went dead dur to seat modules staying on after vehicle shutdown. I unplugged both seat modules and have not had a problem since. I Only plug in to reset seats.