About battery life...

[Mr V]

Originally Posted by 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.

Discharging the battery until it reaches 10.2v permanently damages the battery and should not be done, anything below 10.5 (or 11.0v depending on battery mfg) is considered battery abuse. For max life do not discharge below an open circuit voltage of 12.0v aprox 50% SOC.