Spotlight Cam Battery solar charging both battery

Hi,I'm planning to purchase the Ring Spotlight Cam Battery with solar panel and 1 additional battery pack. I understand the camera will automatic switch to the backup battery if the first battery drained completly. I would like to know if the solar panel will charge both battery? or does it charge only the active battery? For example, if I have both batteries in the unit called battery A & B. If the camera drained the battery A and switched to battery B at night. In the morning, would the camera know how to charge the battery A which is not the active battery now. I could not locate this information anywhere. I appreciate your help.