I’ve got a battery-free efficient keyboard already… it uses this cable connected to the computer to supply power when keys are pressed. Very energy efficient. Never needs to charge. And unlike these keyboards with a built-in lithium battery, it will last indefinitely.
Good point; I’ve used a USB extender that had WiFi at either end to handle the distance thing. Maybe it’s just me, but outside of laptops I don’t generally have a need to move my keyboards around much.