If it were my ass up in the air, I think I would prefer that the electric power to the drive motor(s) be provided by a very reliable Diesel-cycle or external combustion generator and not just a battery pack, at least with our current generation of battery technologies. #2 fuel oil is far more energy-dense than any battery that I can afford.
Agreed. Aviation diesels typically burn Jet-A (widely available at airports, obviously) which is similar in energy content to #2 (and about 50x the energy content of Li-ion batteries on a J/g basis).
As far as I know, the major difference between Jet-A and #2 is that is has a much lower gel point than even the northern winter diesel fuels, because higher = colder. If you already have electric motors, wouldn't electrically heated fuel tanks suddenly be more possible than trying to divert waste heat out of fuel-burning engines?
You could save a LOT of money on fuel if you could use off-road #2 oil instead of Jet-A.
Dry adiabatic lapse rate is approximately 3C per 1000'. I regularly fly at high VFR altitudes or low flight levels in my private (gas, piston IC) airplane.
Even confining yourself to 15K feet, you'd be ~45C or 81F lower than the sea-level temp (assuming the air was totally dry, so maybe call it 35C or 63*F). The wings are extremely effective radiators, and wet wing tanks have fuel right against the outer wing surface.
So, you're going to need to dump an enormous amount of energy into the fuel to keep it heated and non-gelled, which is why we have Jet-A, and in fact many jets need to add Prist anti-icing agent, and even some high-flying piston engine airplanes run their avgas through oil-to-fuel heat exchangers.
So, even if you're going to fly your diesel engine (or diesel generator) airplane in the mid-teens, you're probably still going to want to use Jet-A, both for its superior anti-gel properties but also because of the supply chain dedicated to getting Jet-A to a great many airports where you'd want to operate from.
