FWIW, the Lux Geo can run on on 24VAC, AA batteries, or micro-USB. I don't know how long the batteries last though.
There are lots of reasons why most fancy thermostats need a lot of power. For example, a fancy screen is hungry, WiFi is an expensive protocol (e.g. as compared to ZWave), etc.. Compare the Lux screen to the Nest, and you'll see at least one reason why they think they can get away with batteries.
There are lots of reasons why most fancy thermostats need a lot of power. For example, a fancy screen is hungry, WiFi is an expensive protocol (e.g. as compared to ZWave), etc.. Compare the Lux screen to the Nest, and you'll see at least one reason why they think they can get away with batteries.
Another option, patented by Honeywell I think, is called "power stealing." Here's an interesting article on the subject: https://www.ecobee.com/2014/01/the-problem-with-power-steali....