Good battery technology is obviously very exciting - as an area of research - but it's not something specific to flight.
If I had to give it to someone, I'd give it to something "dumb" - bolting an internal combustion engine to a generator and then using that to drive a quadcopter.
It's "dumb" because you have a generator (weight) to convert mechanical power to electrical power (inefficient) to then send it to a motor (more weight) to convert it back to mechanical power (more inefficiency).
And the reason why I want to call it out is because it's exactly that "dumb" thing that nobody thinks to try, because it's "dumb".
But now the reason why it's actually smart is because it allows an internal combustion engine to be a drop-in replacement for a battery.
The reason why it's smart is because there's an entire ecosystem around electrical propulsion. Motors, motor controllers, flight control units, etc are all being built and perfected around electricity and batteries. Anything that takes you back to shafts or other mechanical drive mechanisms risks putting you alone in your own little corner.
He was swapping between engine and battery and doing runs with both. He said the engine is a little bit heavier than the battery, but has better range.
IMO this is really smart because he's able to see past the obviousness of it being dumb.
