A hybrid storage battery comprising a plurality of combined type batteries connected in series to each other and each comprising an organic solution based battery using an organic solution as electrolyte that is connected in parallel to an aqueous solution based battery using a aqueous electrolyte as electrolyte, wherein: the organic solution based battery and the aqueous solution based battery have average discharging voltages approximate to each other in such a way that when the hybrid storage battery is connected to a load, both batteries can drive the load upon discharging, and are so designed that an abnormal overcharging voltage of the organic solution based battery is higher than a final charging voltage of the aqueous solution based battery and a final charging voltage of the organic solution based battery is lower than the final charging voltage of the aqueous solution based battery; the organic solution based battery becomes overcharged if it is charged beyond its final charging voltage, and gets into an abnormality if it is charged beyond its abnormal overcharging voltage, and the aqueous solution based battery becomes overcharged if it is charged beyond its final charging voltage; and when each of the plurality of combined type batteries is supplied with sufficient overcharging energy to get the organic solution based battery to become overcharged, the aqueous solution based battery is configured to carry out a decomposition reaction of the aqueous electrolyte to absorb the overcharging energy so that a charging voltage of the combined type.battery is suppressed to the final charging voltage of the aqueous solution based battery, thereby preventing the organic solution based battery from reaching its abnormal overcharging voltage. the organic solution based battery and the aqueous solution based battery have average discharging voltages approximate to each other in such a way that when the hybrid storage battery is connected to a load, both batteries can drive the load upon discharging, and are so designed that an abnormal overcharging voltage of the organic solution based battery is higher than a final charging voltage of the aqueous solution based battery and a final charging voltage of the organic solution based battery is lower than the final charging voltage of the aqueous solution based battery; the organic solution based battery becomes overcharged if it is charged beyond its final charging voltage, and gets into an abnormality if it is charged beyond its abnormal overcharging voltage, and the aqueous solution based battery becomes overcharged if it is charged beyond its final charging voltage; and when each of the plurality of combined type batteries is supplied with sufficient overcharging energy to get the organic solution based battery to become overcharged, the aqueous solution based battery is configured to carry out a decomposition reaction of the aqueous electrolyte to absorb the overcharging energy so that a charging voltage of the combined type.battery is suppressed to the final charging voltage of the aqueous solution based battery, thereby preventing the organic solution based battery from reaching its abnormal overcharging voltage.