Our scouting team has transitioned to an iPad app written by a team member (
check it out here!) so power in the stands is crucial for us which is why we bought a deep cycle marine battery and a fairly beefy inverter 750 or 1000 watts IIRC. Its enough to charge 8+ iPads and run a Mac Mini and a monitor all at the same time. The battery will typically last a day of competition and we charge it with our robot batteries over night. We also keep a robot battery and a smaller inverter on our robot cart to charge the driver station.