Petrol is very safe for the energy density it has due to the relatively slow rate at which outside oxygen gets fed into the flame causing a burn rather than exp

Petrol is very safe for the energy density it has due to the relatively slow rate at which outside oxygen gets fed into the flame causing a burn rather than explosion. TNT is far less energy dense (1/5 iirc) but because it contains oxygen it is far more dangerous and explosive. A very high energy density battery is likely to be closer to TNT in its reaction and not have the requirement of needing outside oxigen to keep the reaction speed in check (but really this depends on the exact technology of the battery)