As I said in post #22, anything that has electronics requires a continuous stream of relatively clean electricity and switches that are reliable. Rotax 912 iS in theory gets around the Diamond problem by having a dedicated engine alternator A and an airframe power alternator B which also charges the battery. A and B are tied together at engine start, then separate with A powering ECU’s ignition, injections and fuel pumps. If A fails, B takes over instantaneously and dumps the airframe load and battery charging. There is also a dedicated battery only mode, but I’m not sure if that automatically fails over if both alternators fail.
Moral: you want a battery good for at least 30 min if everything goes wrong.