Mercedes-Benz 2007 SL 55 AMG Operator's Manual page 397

Practical hints
Replacing SmartKey batteries
3 Batteries
4 Contact spring
Pull out batteries 3.
Using a lint-free cloth, insert new bat-
teries 3 under contact springs 4 with
the positive terminal (+) side facing up.
Return battery compartment 2 into
housing until it locks into place.
396
Slide mechanical key 1 back into
SmartKey or SmartKey with
KEYLESS-GO*.
Check the operation of the SmartKey
or SmartKey with KEYLESS-GO* as well
as the KEYLESS-GO* function.