Personally I would rather they had to make phones a little thicker again to include a properly sealed battery compartment, the new ones look very nice but it's too hard to get a decent grip without accidentally bumping the edge of the screen.

Maybe the whole back side of the phone is the battery, and the two sides are independently watertight? The charger port and usb controller could be on the battery too, that way you can replace it if it breaks or you want to be compatible with a new fast charging specification, and you could charge it independently if you have more than one.