Ring solar flood light recharge battery

Hi,I owned Ring Solar flood light and with the additional back up batter as well. I understand the flood light will automatic switch to the backup battery after 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 battery in the unit called battery A & B. If the flood light drained the battery A and switched to battery B at night. In the morning, will 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.