@catch22roy
Unfortunately, none of Google Nest's cameras and doorbells are designed to be opened up and serviced by customers, and for the battery-powered devices, the batteries are not designed to be replaceable, and Google Nest does not sell batteries (or any spare parts).
However, I did find this thread on Reddit, where one reply describes how to replace the battery, but it's not something you'd want to do just to swap out batteries between charging. Besides, there's no way to charge the battery when it's not in the doorbell.
https://www.reddit.com/r/googlehome/comments/1e4esg7/it_is_possible_to_repair_a_google_nest/?rdt=525...
