May I suggest one or a couple of these items for your battery concern
LINK. I own a few versions which can run laptops for many hours, if you get the larger XPower 1500, one unit can run all the laptops you want and supply power at other events or locations. No cords across lots of steps and convenient.
You could also easily hook an inverter to a robot battery to run 1 or 2 laptops until the robot battery dies, then charge that on lunch in addition to the laptops.