FWIW, the Lux Geo can run on on 24VAC, AA batteries, or micro-USB. I don&#x27;t know how long the batteries last though.<p>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&#x27;ll see at least one reason why they think they can get away with batteries.<p>Another option, patented by Honeywell I think, is called &quot;power stealing.&quot; Here&#x27;s an interesting article on the subject: <a href="https:&#x2F;&#x2F;www.ecobee.com&#x2F;2014&#x2F;01&#x2F;the-problem-with-power-stealing&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.ecobee.com&#x2F;2014&#x2F;01&#x2F;the-problem-with-power-steali...</a>.