Does Nest thermostat need charging?

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. If problems persist, wiring upgrades may be required.