I do not believe that All-Electric or Hybrid-Electric will ever compete head-to-head with traditional jet-fueled HBP engines. Rather, electric flight will fill a different niche, enabling smaller regional flights, probably with slower, lower flight, at a price-point impossible with modern jets.

@Jim I don't know if they did or not. Its pointless to your question. The point is the FAA has approved it for flight (in some form-or-fashion). Why isn't the FAA's approval enough for you? You seem satisfied with their Airworthiness Directives, but not their approvals?

You have confidence in the FAA when they issued an A.D. concerning the engines. Then later, you do not have confidence in the same FAA when they accept that the engine is safe for flight. Seems hypocritical, doesn't it?

@Boeing787: Depending on the plane there is a very good chance that the PFD can already be powered by battery, by APU, or by the alternators on engine 1 or engine 2. Another battery would add a small bit of redundancy, at the cost of added complexity, but leave 500 other failure pathways unchanged.

Its not that the Integrated Standby Instrument System (ISIS) is infallible, its that its failures are unrelated to the main system. ISIS can and will fail from time to time. But its failures should be unrelated to the main instruments, so that one of the systems is always working, and the chances of both failing at the same time is extremely remote.