There are some good battery powered switches, but they don’t actually control the current flow. They just act as wallmount remotes. In the U.K., Devolo and Popp make nice versions of these that will work with SmartThings. But then there has to be some device which actually does cause the lights to go on and off. It could be that the lamps themselves are smart or it could be and in the wall micro, not battery-operated, installed in the ceiling Rose where there typically will be a neutral. So the switch sends a message to the SmartThings hub which then sends the message on to the device that does control the brightness of the Lamp.
Note, though, that all of those are “surface mount” devices which are mounted on top of the wall, not inside it.
The reason why we can’t just hook a battery to the radio that is inside the wall is that pretty much any battery-operated device inside the wall becomes a fire hazard. Safety codes generally prohibit that in both the US and the UK.