Nest uses your HVAC's power wire like other thermostats. There are no batteries to replace. It has a permanent internal battery, charged by the power wire, whi

Nest uses your HVAC's power wire like other thermostats. There are no batteries to replace. It has a permanent internal battery, charged by the power wire, which allows it to stay active in a power failure and to use more power than some systems provide when you're interacting with its screen. So there's no real difference between the Nest and the Honeywell in terms of power or installation except that the Nest has a built-in rechargeable li-ion backup battery. Here's how mine's wired, courtesy the mobile app again: http://i.imgur.com/Rls9EZk.png http://i.imgur.com/Rls9EZk.png