Car makers are preparing to introduce plug-in electric cars in 2010, but their success will depend on players beyond their control: the electric utilities. The plug-ins are a new generation of hybrid cars that can run 10 to 40 miles on electric batteries before they have to tap their gasoline engines. This gives them, on a tank of gas, a driving range of as much as 600 miles without recharges to potentially thousands of miles with recharges.