I'd like to be able to replace the battery in the controller with a spare.
The controller is slow to charge, especially because it simultaneously charge the phone/tablet.
Usually, the day comes to an end because of my inability to quickly charge the controller.
If I could swap the controller battery for a spare controller battery, I could fly for a lot longer.
I am never usually limited by drone batteries - I have 4 of them charging while flying. It is never usually the limiting factor.