PURPOSE: To increase the life and improve the charging efficiency of a lead storage battery by equalizing the concentration of electrolyte by attaching a pressure control value to the top of the battery and providing a means of stirring the electrolyte after opening the pressure control valve when the internal pressure of the battery increases to a given level.
CONSTITUTION: The original internal pressure of a lead storage battery is an atmospheric pressure. A pressure control valve 10 is closed. When the internal pressure of the battery gradually increases due to gas generation and becomes different from the internal pressure of a case 4, electrolyte 3 existing in the lower part of the battery flows through an inflow valve 5 into the case 3. When the internal pressure of the battery reaches 0.01kg/cm2 or greater, the pressure control valve 10 opens. When the internal pressure of the battery becomes an atmospheric pressure again, the electrolyte 3 contained in the case 4 flows out through an outflow valve 8 into the battery. By repeatedly carrying out these processes, the electrolyte 3 of high concentration existing in the lower part of the battery is efficiently carried to its upper part and any stratification of the electrolyte 3 is prevented.