Couldn't these be fitted with enlarged versions of the emergency power turbine to feed some energy back into the batteries? Commercial planes have a small turbine that drops out of the fuselage in the event of an engine failure so that the plane can still use at least some of its fly-by-wire systems and the crew can attempt an emergency landing. Surely the principle could be scaled up to help power these electric planes? Wonder how much extra drag it would create, could end up being more harm than good.