If you now consider that the only way to use that energy is through combustion, and that an combustion engine is only 1/4th as efficient as an electric one, tha

If you now consider that the only way to use that energy is through combustion, and that an combustion engine is only 1/4th as efficient as an electric one, that factor suddenly shrinks to 12.5 - 25 already. Frankly, energy density is a bit of an distraction. If we go by energy density alone, we would presumably all be cruising on Uranium, which energy density is... well off the charts. But there a plenty of good reasons we don't fuel transport with Uranium, and there are just as many good reasons why we shouldn't continue to use gasoline.