wrote:
100LL Avgas is 44 MJ/kg.

Batteries need to be able to produce better than 20 MJ/kg to be
generally usefull for transportation.

The Avgas energy density is not comparable to battery energy density
because it doesn't factor in thermal to mechanical conversion. Current
automobile engines extract only about 20% of that 44 MJ/kg. Electric motors
are anywhere from 75% to 95% efficient in converting electrical power to
mechanical power.

So a battery with ~11 MJ/kg powering an 80% efficient electric motor has
the same usable energy density as Avgas powering an internal combustion
engine.

Setting the goal for battery energy density at 20 MJ/kg would simply be
wrong because it uses the wrong numbers.