those mercs like the C class and all new mercedes cars have a Control unit called SAM Signal Acquisition Module and it controls almost all the electrics of the car. they sometimes go bad and cause batteries to go flat. in the C class as one of the forum membs has found out it cause a new battery to die in 48 hrs. the c class has 2 SAMs one under the fuse box one in the trunk, you need a scanner to be sure thou.

__________________
Jay,
-----------------
-1995 Blue W202 C36 AMG (M) SOLD ;(
-1995 Black W140 S500 (Lady)
-1992 Black W124 E300 (Dima) (Ex-Mosselman
Twin turbo Kit).
-1988 Black W124 300 E 4-Matic.(Nadeen)
-1983 Brown W126 500SEL.(Old Lady)(Sold)
-1981 Gold W123 280CE.(Dareen)(Sold)
http://www.youtube.com/user/jayrasheed