Good luck on a design with no on/off switch. I strongly doubt that either the CPSC or UL would be okay with a system with 48v and 5+ amps that you can't turn off. And I doubt very much that UPS or anyone else would ship them for you.
And your idea, while intriguing, opens up further cans of worms. If you can talk to the bike via an app, that presumes that the bike is visible to bluetooth. Bluetooth does draw a small amount of power and since you have no interface and no way of turning bluetooth off, you would probably drain the battery if you left the bike in the garage for ten days or so. Further questions with bluetooth would include what would happen if you had two bikes like that in front of you? Which one would the app connect to? How could you control that? How could you keep someone else at a coffee shop from connecting to your bike?
It is a nice dream, I suppose. But there is real design work there if you really want to make it work.