There is provided a method for operating a lead acid storage battery in order to compensate for fluctuations in the amount of power generated by a solar power generation apparatus, a wind power generation apparatus, or another natural energy power generation device, the lead acid storage battery being charged by a power generation device and discharged to a load. The state of charge of the lead acid storage battery is maintained in a range of 30 to 90% where the fully charged state of the lead acid storage battery is 100%; and the lead acid storage battery is charged and discharged while the battery voltage is kept in a specified range of 1.80 to 2.42 V per cell to extend the service life of the battery. A reference temperature of 25° C. is established, and when the ambient temperature has risen above or fallen below the reference temperature, the upper and lower limit values of a specified range are corrected within a range of −4 mV/° C. to −6 mV/° C. per cell according to the amount by which the temperature has increased or decreased so that a corrected voltage range is obtained. The storage battery is charged and discharged while the battery voltage is kept in the corrected voltage range, and the battery is operated.