[Mr V]

The battery's life expectancy is expressed in the number of charge/discharge cycles and the number of cycles is directly related to the average depth of discharge. The deeper the discharge lower the expected number of cycles that the battery will last. Also a battery that is stored in a less than fully charged state will tend to develop sulfate deposits at a higher rate than one that is stored fully charged.

So at competitions put your batteries on the charger as soon after each match as possible. When practicing try to avoid letting the battery discharge to the point that you notice a drop in robot performance. When you are practicing have the driver's note the voltage on the driver's station display. Once the battery voltage shows as 11.0 v or lower when the robot is idle it is time to change the battery. Doing both of those things regularly will maximize the useful life of the battery.