my last post and puzzling over some of the esoteric elements I did not see the obvious solution. A post by John Voelker for Green Car Reports proposes the winning answer: measure the range using a unit of energy consumed, in this case kilowatt hours. So very simply the range of a car would be miles/kWh or for those looking for a more elegant answer: kWh/100miles.
As in all new business models (in this case new infrastructure) the answer often lies in out-of-the-box thinking.
Hopefully the EPA is reading this.