PURPOSE: To lengthen water replenishing intervals, to save electricity, to restrain temperature rise, to realize a high capacity battery, to prevent electrolyte stratification, and to increase reliability, by using a battery equipped with an electrolyte stirring unit and by limiting the charging amount to a necessary minimum value.

CONSTITUTION: The lower end of an electrolyte stirring unit D is positioned in the bottom of a container A and its lower end opening is positioned in the lower part than a small hole 4 of an electrolyte circulation cylinder 1, and a gas collecting chamber 2 for collecting gas generated from a plate group B is equipped. An electrolyte within a reverse U-shaped siphone strap is returned to the cylinder 1 from the small hole 4 according to accumulation of gas into the chamber 2. When the amount of accumulated gas reaches the position of the small hole 4, gas is pushed out as bubbles into the cylinder 1, and gas bubbles push up the electrolyte existing in this place in the cylinder 1 and rises, then exhausted together with the electrolyte from an upper end opening of the cylinder 1. At the same time, the pressure of the electrolyte in the cylinder 1 is reduced and the electrolyte in the bottom of a battery enters into the cylinder 1 and rises. The electrolyte with large specific gravity is pushed up to the upper part than the small hold 4 and stabilized in the position where it is balanced with the pressure of the electrolyte existing around the cylinder 1. These operations are repeated.