ELECTRICAL STORAGE DEVICE, ELECTRONIC INSTRUMENT, POWER SYSTEM, AND ELECTRIC VEHICLE

An electric storage device includes an electric storage unit that includes one or a plurality of electric storage elements, a measurement unit that measures voltage, a current, and a temperature of the electric storage element, and a calculation unit that calculates internal resistance of the electric storage element based on the voltage, the current, and the temperature measured by the measurement unit. When a determination unit detects discontinuity of temporal variation of the calculated internal resistance, it is determined that the electric storage element has been exchanged. Since the electric storage element such as a lithium ion secondary battery has such a characteristic that the internal resistance increases as the number of use is increased, the exchange of batteries can be detected from the change in the internal resistance.