About battery life...

[cheesepuffgd]

1. Don't store your batteries in a discharged state.
2. If you can, discharge(from a fully charged state) each one of your batteries over a 20 watt load until they are at 10.2 volts. Charge the battery immediately afterward. This can be done with a DC lightbulb and a voltmeter.
3. Doing this about once per season will keep your batteries lasting for years(my team still has a battery from 2009 that works for practice). Measuring how long this discharge takes will allow you to calculate the capacity of the battery in watt-hours. If the capacity dips below about 100 watt-hours, the battery probably won't work well at competition.
4. A watt-hour meter on the robot during a match or a simulation of a match(driving the robot around sporadically using its special systems for 2.5 mins) may give you an idea of how many matches a battery can be used in.