Great question John. I think the theory goes like this: Airplanes need 100% power for takeoff. They need about 90% for climb, and about 80% for cruise. So if you design an airplane with a slightly smaller engine that flat-out produces 85% of the power needed, the fuel consumption is 15% less than an airplane with a full-size engine. You let the engine run flat-out all the time. During the takeoff, you’ll need the extra 15% energy to come from an onboard battery. During climb, you’ll need to supplement the engine by 5% with energy from the battery. During cruise, the generator is capable of powering the airplane fully and also slightly charging the battery. During descent, the props can recover energy to charge the battery (and the generator still running flat out is aggressively charging the battery). So the battery is charged and available for a potential go-around at the destination, or possibly ready for the next flight not long after landing.