[aidenn0]

Nitromethane engines are less than 50% efficient and batteries are already about 10% as dense as nitromethane, so it's less than a factor of 5 difference.

For drag, the limit is more likely to be power density rather than energy density (same reason why more energy dense gasoline isn't used in top-fuel; the limiting power factor for a typical ICE is the amount of air you can get in the cylinder and you get about double the power with nitromethane vs gasoline for a fixed amount of oxygen).

[edit]

The power you can get with nitromethane is only double if you run stochiometric; since it is partially self-oxidizing, running richer lets you get even more power (sources seem to indicate 4x). Of course running rich lowers the efficiency even more.