Well, in this case, we don’t need to argue about theory. The Joby has a tested range of 150 miles. They also tested it with hydrogen fuel cells and got >500.
Sounds about right. A plane of comparable max take-off weight, a Piper Malibu, has a range of ~1500 miles (with reserve remaining).
Right, so when you factor in the legally required reserve flight time the battery powered Joby is only capable of very short hops. And that's fine, it's still potentially useful on a few routes and newer models will improve over time.