US Patent 9614258 Power storage device and power storage system

To provide a power storage device, an operation condition of which is easily analyzed. A secondary battery includes a sensor that is a measurement unit, a microcontroller unit that is a determination unit, and a memory that is a memory unit. With the sensor, conditions of the secondary battery such as the remaining battery power, the voltage, the current, and the temperature are measured. The microcontroller unit performs arithmetic processing of the measurement results and determines the operation condition of the secondary battery. Further, the microcontroller unit stores the measurement result in the memory in accordance with the operation condition of the secondary battery.