I got that kind of mileage from my Volkswagen Jetta diesel back in the 70's.
Now we're to have orgasms because an ultra expensive battery will push a lightweight car 40 miles and then the engine comes on to recharge the battery?
Something is missing from this scenario.
To GM: good luck selling these.
Clarification: The Jetta would go about 600 miles on a tankful of diesel (about 14 gal IIRC). It worked out to about 54 miles per gallon. I loved the ability to drive and drive and drive and drive. My wife and daughters brought me back to earth by pointing out that occasional stops are mandatory.