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 32°F (0°C), and will charge slowly at temperatures near freezing.
Cold weather battery charging behavior in Nest cameras and doorbells.
Nest Doorbell (battery)
Typical: It takes approximately 5 hours to fully charge the battery using a compatible 7.5W AC adapter (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.