PURPOSE: To suppress the power consumption quantity of a pump by connecting a pressure sensing resistor decreasing its resistance value when a pressure is applied between a pump and a battery main body in the water injection type battery provided with the pump forcibly feeding sea water or fresh water into the battery main body.

CONSTITUTION: A three-way cock 3 with a valve 4 is provided at a feed port of sea water or the like to a battery main body is provided, a pump 5 feeding sea water or the like is connected. The valve in the three-way cock 3 is located on the pump 5 side when the pump 5 is not operated, sea water or the like freely enters into the battery from another inlet of the three-way cock 3. When the pump 5 is operated, the valve closes the other gateway of the three-way cock 3 by the pressure of the pushed-out sea water or the like, the sea water or the like fed from the pump 5 enters into the battery main body. A pressure sensing resistor 6 decreasing its resistance value when applied with a pressure is connected on one side between the output terminal of the battery main body and the input terminal of a motor. The power consumption quantity of the pump is thereby reduced.