Hi!
One easy way to implement the selection of the power source could be the "toggle cameras" menu, where you can switch cameras on- or offline.
In this menu there could be the option to switch the battery on- or offline.
As other technical devices drain power too (not implemented in the game yet), it would be cool if they also could be switched offline while not in use.
I toltally agree with that.
Cheers and big up to the developers! Great game :)