Actually, that UI is pretty much exactly what I had in mind. All devices that control their own charging should have that "trip" switch. It's a shame that Android does not have an API to customize charge depth like that. I occasionally spend some idle thought on wondering how difficult it would be to overcome this limitation with a bluetooth-controlled charger. Well, I'm not an electrical engineer and "bringing the joys of self-asphyxiation to your phone" maybe would not be the most successful kickstarter ever either.
Most decent smartphones are already doing battery management and avoiding extreme draining or charging of the cells.
Think about it this way: If your phone has 8 hours of use, chances are the battery could really give you 9 or 10 hours if it was fully charged, but the manufacturer is software limiting it to prolong the life of the battery.
All things with a LiIon battery do battery management to avoid extreme draining or charging. I've never seen a phone that offered a choice of "more battery cycles vs slightly longer run-time".
For cars, it's not an unusual feature to be able to choose. The Leaf has that feature, and since it cycles its small batter frequently, it's an important consideration for owners. See:
No phone allows me to further reduce the voltage range in order to have a runtime/durability tradeoff other than the one the manufacturer selected to maximise replacement after 24 months.
