so basically, you have a main power storage, and a few other mini power storages, each one doing their own thing, like powering the lights for the building, or the door, or cams, etc. you can direct some power from the main power storage to the little power storages, like move 5% of you main power to your light, or 35% to the vent snares, etc. when you use the door, the door power will go down, and you'll need to take power out the main power storage to power it, same with all the others. you can recharge your main power with a setting on the cams, but slowly. if that main power storage runs out you'll have nothing to power the doors and that, but the power still in the door power storage will stay unt1l used.

hope that made sense