US Patent 7253585 Battery pack

A method for conducting an operation including a power tool battery pack. The battery pack can include a housing, a first cell supported by the housing and having a voltage, and a second cell supported by the housing and having a voltage. The battery pack also can be connectable to a power tool and be operable to supply power to operate the power tool. The method can include discharging one of the first cell and the second cell until the voltage of the one of the first cell and the second cell is substantially equal to the voltage of the other of the first cell and the second cell.