The safest and most established method to test the capacity of a battery is the discharge test.

The battery system must be completely charged before this test, which starts by discharging the battery in a steady intensity as indicated by the manufacturer. This is done until the tension of the battery is similar to an uncharged battery.

The time needed to reach this minimal tension multiplied by the intensity results in the current capacity. In determined periods, the tension of the cells is measured. This information has special importance because it reveals the weak cells.