Mercedes-Benz B-Class Electric Drive W245 Operator's Manual page 77

Make sure that the surface of the battery is
X
free of lint, grease and other contaminants.
Insert the front tabs of battery tray cover :
X
and then press to close it.
Insert the mechanical key into the Smart-
X
Key.
Check the function of all SmartKey buttons
X
on the vehicle.
SmartKey
75
Z