A method and article of manufacture for monitoring an electrical energy storage device adapted to supply electrical power to a selectively actuable electric motor is described. This comprises determining a state of charge and a temperature of the electrical energy storage device subsequent to a stabilization period, and measuring a minimum voltage output from the electrical energy storage device during selective actuation of the electric motor. One of a plurality of predetermined threshold voltage states is selected based upon the state of charge and the temperature. The minimum voltage is compared to the selected predetermined threshold voltage.