The Nest thermostat charges its batteries using the wires of your heating and cooling system, so you shouldn't have to do anything. But if there is a problem, the battery can drain. If that's the case, pop off the display, and plug it into a power source using a micro-USB (Micro-B) to USB-A cable. Note, if you have a first generation Nest Learning Thermostat, you will need to use a mini-USB (Mini-B) to USB-A cable. If the battery is completely drained, it can take up to two hours to recharge.
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