See also:

Problems with the SmartKey
Problem Possible causes/consequences and Solutions You cannot lock or unlock the vehicle using the SmartKey. The SmartKey battery is discharged or nearly discharged. ...

Releasing the parking lock manually
In the event of an electrical malfunction, it is possible to release the selector lever lock manually to move it out of position P, e.g. if you wish to tow the vehicle away. Do not use any s ...

Parking the vehicle for a long period
If you leave the vehicle parked for longer than four weeks, the battery may be damaged by exhaustive discharge. - Connect a trickle charger. You can obtain information about trickle charg ...