They have one of the best efficiency motor and controllers available, and they do not use BMS, and the drivetrain has no 90º turns in it. There may be other factors, but those are the ones I remember Kevin Smith mentioning.
As I understand it, typical plug-to-wheel efficiency is ~85%.
The X-Prize version of Seven was in the neighborhood of 156Wh/mile at 60mph, and not it is ~129Wh/mile at 60mph. They now have a sweet reduction gear:
Compared to the one they chewed:
