Batteries are usually wh/kg since wh is what you use for battery capacity. You have to watch it with fuel energy density since it normally doesn't take into ac

Batteries are usually wh/kg since wh is what you use for battery capacity. You have to watch it with fuel energy density since it normally doesn't take into account the efficiencies of converting it to useful work and the equipment weight needed, its just the heat energy released when burned. Electrons probably have a really high wh/kg. A battery has power leads coming out of it to give you electricity and modern electric motors are above 90% efficiency at converting to mechanical energy. Diesel needs fuel tanks and a heavy engine and more complicated and heavy transmission as well. The engine itself is probably under 40% efficient at converting those MJ to horsepower. Same goes for fuel cells they are similar in efficiency to ICE and have weight and say with hydrogen storage you need heavy tanks and protective structure to hold safely. Also with hydrogen it has low volumetric density so even though it has good MJ/kg it has low MJ/L relative to say Diesel. All current fuel cell cars are similar in weight to a BEV and seem to have just a slight range advantage with big power disadvantage. Now look at the efficiency of creating hydrogen at I am very skeptical of it becoming mainstream anytime soon.