How many batteries do you think 3 rigs would need for the day, and into the evening? I'm so used to just being able to charge.I've used a portable power supply to run my charger at other events.
Something like this will let you charge plenty of times over the weekend:
Anker Portable Power Supply
But if you are only going to be there for a day, it is probably easiest to charge what you need at home.