[jeffh]

Most of the car share companies operate this way near me. It's not "exclusively via app", but most people rely on the app and NFC to unlock/start and lock/end their trips for convenience.

That said ... you are in a car that can charge your phone too.

[BadassFractal]

In my case the issue wasn't battery, it was the phone locking up and no "reset combination" for it would reboot it.