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.
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: To help prolong the life of your doorbell's battery, it will only charge to 75% 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 75%. However, after the doorbell is wired to the system, the battery will drop down to 75% and stay at that level or below.