Well, electricity is certainly cheaper to charge a car battery than it is to buy gasoline to travel the same amount, and cheaper price for a commodity generally implies uses less energy. Does your gallon of gas take in to account the cost of driving it around the country instead of being transmitted over power lines? A quick google search found that there's only a 6-8% loss in power in transmitting the energy across the power grid, but only 30-40% of the energy contained in coal can be turned into electricity. That is more telling of coal power plants than the general principle of charging cars off the grid.