The battery pack including a battery group in which a plurality of secondary batteries are connected in series; a detector that detects a charging and discharging current value flowing in the battery group and a voltage value of the battery group in a time-division manner by switching between the current value and the voltage value using an electronic circuit; and a controller/operator that performs operation and control using the current value and the voltage value detected by the detector. In the battery pack, the detector detects current values before and after the voltage value of the battery group is detected, and the controller/operator determines that the voltage value of the battery group is influenced by the peak discharge power when at least one of the current values exceeds a predetermined threshold.