Note that the Range Extender is $600. The web page http://www.mbusa.com/mercedes/vehicles/model/class-B/model-BED#businessType=DEALERS states:
Temporary range extender
A suite of options to further increase your driving range includes added insulation of the doors and roof for to increase climate-control efficiency, along with an electrically heated windshield and a range-extending charge function. By pressing a button on the console prior to charging, the maximum charge level for battery will increased for the next charge cycle. The higher-capacity charge can provide up to 17 additional miles of range.
It appears that the Premium Package and the Multimedia Package are linked. I could not choose one and not the other!