GENERAL MOTORS introduced America to the Chevrolet Volt at the 2007 Detroit Auto Show as a low-slung concept car that would someday be the future of motorized transportation. It would go 40 miles on battery power alone, promised G.M., after which it would create its own electricity with a gas engine. Three and a half years — and one government-assisted bankruptcy later — G.M. is bringing a Volt to market that makes good on those two promises. The problem is, well, everything else. For starters, G.M.’s vision turned into a car that costs $41,000 before relevant tax breaks ... but...