What do Detroit billionaires do with their cash after they retire from the upper echelons of the auto industry? The answer, in the cases of Lee Iacocca and Robert Stempel, may surprise you: They start electric-car companies. Stempel, the former head of General Motors, helped create the emissions-reducing catalytic converter in 1966 and has always had a bit of an environmental bent. Now, as chair of Energy Conversion Devices, he is developing a prototype electric car — one that will be a “real vehicle,” he noted, as opposed to electric cars designed to go at slow speeds for short distances. The latter is more the territory of former Chrysler CEO Iacocca — who, unlike Stempel, has been drawn into the electric-vehicle market by the profit motive, not by an environmental ethic. As founder and president of Lido Motors USA, Iacocca is selling a neighborhood electric vehicle that can go 25 mph and travel for up to 40 miles on a six-hour charge. He hopes the car will catch on among early retirees and residents of gated communities.