That's unfortunately a big part of why mine is dead. The batteries are hard to get to. Also their iOS app is frustrating to use.

Could maybe be made low enough power that it can power itself via ambient light (like an old school calculator) or radio waves.

That would be cool, but I haven't actually seen it in anything other than an old school calculator so I assume the limitations are pretty significant.

I've seen energy-harvesting remote light switches for sale — they supposedly get enough energy from the physical act of flipping the toggle to send a few radio packets. I haven't used one in the real world though.

Some of the ones at my company require you to stab them with your fingers for 15 seconds like a maniac before they turn the light on.