An iPad has an extremely good battery and will last for quite a while. Our testing has shown that an iPad can be used running the iKeypad app for 10-12 hours on a single charge depending on the length of the sessions and the time between sessions. To achieve this, you need to eliminate any unnecessary functions of the iPad that would drain the battery. Apple has some good information here.
You might want to have portable battery chargers, capable of charging your iPads, available for each event in case the battery runs out before the end of the session.
This will test your expertise on Phone Batteries.
The quiz is provided by AT&T - please: Click Here (13 Questions)
iKeypad - Score entry
Flatscreen TV - Score displayed