Hmm... it seems like the really sweet spot for this type of thing is one that could supply power while you drive. If it could deliver about 7 kW (a little more than the mains plug for a domestic dryer or oven or range), it would supply around 50% to 70% of the car's freeway power requirements. That would double or triple the range, from ~250 miles to ~750 miles.

well, at least it exists. When going to family for the weekend, I could at least have it charged by time we go home. That being said, they'd have to let me have the garage, and we couldn't really use my car while there. Still a hassle, but it could be worse I guess.