One more quick thought on EVs

I got hit with what my correspondent must have thought was a great burn: Fossil fuels can achieve an energy density of up to 48MJ/kg, LiIon batteries on the other hand run to about 0.7MJ/kg. 

I just finished writing back to them. 

Fossil fuels achieve their 48MJ/kg energy density ONLY ONCE, Li-ion batteries over and over again. One is a primary energy production technology, the other is a storage technology, it's comparing apples to oranges. 

If you were to consider the 0.7MJ over the lifespan of  batteries, they can achieve a cumulative energy density of 240MJ/kg. 

Point goes to EV technology I think.