Hybrid system--??
What about a hybrid system to get around battery limitations, perhaps?
Fit a battery that's just large/heavy enough to provide perhaps 10 minutes of power for takeoff and initial climb, along with a small turbine, say APU size.
Then established in cruise at constant power demand, start the turbine, which would solely power a generator to recharge the battery. Seems to me constant power demand at peak output would reduce the inefficiencies associated with the turbine engine operation and this hybrid plant would be very efficient and reliable.
Thoughts?