Mercedes-Benz CLA Operator's Manual page 77

Repeatedly tap the SmartKey against your
X
palm until battery = falls out.
Insert the new battery with the positive
X
terminal facing upwards. Use a lint-free
cloth to do so.
Make sure that the surface of the battery is
X
free from lint, grease and all other forms of
contamination.
Insert the front tabs of battery tray
X
cover : and then press to close it.
Insert the mechanical key into the
X
SmartKey.
Check the function of all SmartKey buttons
X
on the vehicle.
SmartKey
75
Z