Google Nest camera and doorbell battery charge time depends on several factors, including ambient temperature and the state and condition of the battery. The battery won't charge at temperatures below 0°C (32°F), and will charge slowly at temperatures near freezing.
Cold weather battery charging behaviour in Nest cameras and doorbells.
Nest Doorbell (battery)
Typical: It takes approximately 5 hours to fully charge the battery using a compatible 7.5 W AC adaptor (sold separately).
Important: The doorbell's battery charges to 100% the first time you charge it. To help prolong the life of the battery, it will only charge to 80% if the doorbell is wired to the doorbell system. Before you install your doorbell, you can use the USB cable to charge the battery above 80%. However, after the doorbell is wired to the system, the battery will drop down to 80% and stay at that level or below.
Nest Cam (battery)
Typical: It takes approximately 5 hours to fully charge the battery using the provided 7.5W AC adapter and charge cable.
Important: The camera's battery charges to 100% the first time you charge it. To help prolong the life of your camera's battery, it will only charge to 80% if the camera is connected to a continuous power source during use. Before you install your camera, use the USB cable to charge the battery above 80%. However, after the camera is set up and plugged into a power source, the battery will drop down to 80% and stay at that level or below.