Mercedes-Benz 2008 CLS 550 Operator's Manual page 404

3 Batteries
4 Contact springs
Pull out batteries 3.
Using a line-free cloth, insert new bat-
teries 3 under contact springs 4 with
the positive terminal (+) side facing up.
Return battery compartment 2
( page 402) into housing until it locks
into place.
Slide the mechanical key back into the
SmartKey/SmartKey with
KEYLESS-GO*.
Check the operation of the SmartKey/
SmartKey with KEYLESS-GO*.
Practical hints
Replacing SmartKey batteries
403