On vehicles with airmatic suspension, the airmatic pump relay can stick, causing a dead battery, because the pump continues to operate when it should be shut off. Eventually, the pump will fail; the pump, fuse, and relay will need replacement.
Car Problem Reports
Mercedes-Benz S350 Airmatic Pump Relay May Stick and Cause Dead Battery
Mercedes-Benz S350 Problem
Model Year Affected: 2006
Visitor, 2006 Mercedes-Benz S350, 41,000 mi
Airmatic pump would keep running even long after turning the engine off. Disconnected battery to turn the pump off. Had relay and fuse replaced. The very next day pump failed and had to replace it.