As a simulation load is driven with an object cell, a cell discharge stop voltage is estimated by collecting data of a discharge current and a terminal voltage, processing the collected data to obtain an approximate linear function between the discharge current and the terminal voltage, substituting a first reference value into the linear function to estimate a first voltage, making a decision for the first voltage having reached a second reference value, responding to the decision for substituting a third reference value into the linear function to estimate a second voltage, and outputting the second voltage as a representative value of the discharge stop voltage.