Patent ID: 8436585

Claim:
A power supply device comprising: a rechargeable battery pack; a charging/discharging control portion that controls charging/discharging operation of the battery pack; a current detecting portion that detects charging/discharging currents flowing in the battery pack; and a battery capacity calculating portion that estimates the remaining capacity of the battery pack based on the charging/discharging currents detected by the current detecting portion, wherein the charging/discharging control portion is configured to select one of a plurality of control modes, the charging/discharging operation being controlled based on the selected control mode, the control modes comprising: a charging operation disabled mode for disabling the charging operation when the remaining capacity estimated by the battery capacity calculating portion is higher than a predetermined control upper limit; a discharging operation disabled mode for disabling the discharging operation when the estimated remaining capacity is lower than a control lower limit, the control lower limit being specified lower than the control upper limit; and, a charging/discharging mode for the charging/discharging operation when the estimated remaining capacity is between the control upper limit and the control lower limit, wherein the charging/discharging mode further comprises: an allowance mode where the charging/discharging control portion is configured to control the charging/discharging current limit values to allow a discharging amount to exceed a charging amount in a predetermined period when the estimated remaining capacity is higher than a range upper limit of a given range, the given range being defined by the range upper limit and a range lower limit predetermined in a state of a charging, the allowance mode being conducted until the estimated remaining capacity being beyond the given range drops to a target state value or lower, the target state value being defined at a center of the given range, and a restriction mode where the charging/discharging currents are restricted to hold the remaining capacity within the given range when the estimated remaining capacity is lower than the range upper limit of the given range, wherein an excess discharge allowed range in the state of charge that corresponds to the allowance mode for the charging/discharging operation is higher than the given range applied for the restriction mode.