Power storage system

A power storage system comprising:

• a battery;
• a voltmeter configured to measure voltage of the battery;
• an ammeter configured to measure current of the battery;
• and
• processing circuitry, wherein
• the processing circuitry functionally includes:
• a first calculation unit configured to calculate estimated internal resistance, which is an estimated value of present internal resistance of the battery, based on the voltage and the current;
• a second calculation unit configured to calculate discharging power upper limit, which is an upper limit on discharging power for the battery, based on the estimated internal resistance calculated by the first calculation unit, the present voltage, and the present current;
• a discharge control unit configured to control discharge of the battery to prevent discharging power exceeding the discharging power upper limit from being discharged from the battery;
• and
• a limitation unit configured to determine, based on the current, whether power fluctuation in which output power of the battery fluctuates greatly within a short period of time has occurred or not and to prohibit the second calculation unit from operating during the power fluctuation.