Yes of course, I meant to say 1 kW·h = 1 kg; but I'm not certain if I remember correctly now; I could be off by a factor of 10 I guess. It was either 1 kg battery weight = 1 kW·h, or perhaps he said 10 kW·h had to be contained in a 1 kg battery to allow all types of air travel.

I think the 100 kW·h Tesla batteries found in the Model S/X weigh around 750 kg; so I guess electric air travel is still difficult unless a battery breakthrough happens; at least in terms of weight.