I get it; I ran into the same problem. All you have to do is buy energy drinks and consume them while you're with her. To give you an idea, your stamina level determines how much "charge" the camera has for the nighttime sections.
Isn't it easier to just say "your stamina is camera battery at night"?
So instead of buying energy drinks, simply go running to increase max stamina and make sure not to start the night when your stamina is low
Sure energy drinks replenish some stamina both during the night and running but the main problem is that he didn't make the connection between stamina and camera battery at night