Gasolina!!

Curiosidades da wikipédia:
In terms of energy density, existing commercial electric double-layer capacitors range around 0.5 to 30 W·h/kg, with the standardized cells available from Maxwell Technologies rated at 6 W·h/kg and ACT in production of 30 Wh/kg.[6][7] Note however that ACT’s capacitor is actually a Lithium ion capacitor, known also as a “hybrid capacitor”. Experimental electric double-layer capacitors from the MIT LEES project have demonstrated densities of 30 W·h/kg and appear to be scalable to 60 W·h/kg in the short term,[8] while EEStor claims their examples will offer capacities about 400 W·h/kg. For comparison, a conventional lead-acid battery is typically 30 to 40 W·h/kg and modern lithium-ion batteries are about 160 W·h/kg. Also, gasoline has a net calorific value (NCV) of around 12,000 W·h/kg, which in automobile applications operates at 20% tank-to-wheel efficiency giving an effective energy density of 2,400 W·h/kg.

Gasolina!! Só é pena é desperdiçar-se 80% da energia porque o motor é ineficiente!