"Energy density" for this discussion is actually specific energy, ie energy per unit mass.

Energy density (energy per volume) also matters for aviation but energy density is the real kicker...

Batteries will never have energy density comparable to kerosene. Chemistry is based on physics... electron valance energy isn't changing, at least not in this reality. There are no big surprises left in the stable (non-radioactive) areas of periodic table, or Newtonian physics.

Max *theoretical* specific energy for electro-chemical storage is ballpark 1000 WH/Kg. Current battery technology can actually utilize maybe 250 WH/Kg. That's at the cell level, you lose some in the packaging and battery management. Maybe they can get that up to 800WH/Kg someday?

Kerosene's specific energy is 12,000 WH/Kg...

Batteries can *someday* plausibly be used for smallish regional aircraft on stage lengths of a maybe a couple hundred NM. Bigger or longer than that, an you need liquid fuels.

H2 has a very good specific energy, better than kerosene actually. But it falls short on *energy density*... it takes up a huge volume, so you need a huge airframe to hold that volume, and that's heavy and expensive, so you need more fuel, etc.

Remember the Saturn V? That burned kerosene. Space shuttle on the hand burned H2, and needed that big orange external tank to carry enough.




Yes they absolutely have a practical niche, they were phased out because pax didn't like them. A new generation with an emphasis on low noise and vibration might be a renaissance.