Mercedes-Benz S-Class 2012 - Manual (Page 85)

X Make sure that the surface of the battery is
free from lint, grease and all other forms of
contamination.
X Insert the front tabs of battery tray
cover : and then press to close it.
X Insert the mechanical key into the
SmartKey.
X Check the function of all SmartKey buttons
on the vehicle.
SmartKey
83
Opening/closing
Z