PURPOSE: To remarkably lengthen the life of a lead-acid battery by using a positive grid practically free from antimony, adding a specified percent or more of a conductive additive to a negative active material, and limiting the maximum charging current to a specified value or higher.

CONSTITUTION: A conductive material such as carbon is added to a negative active material 0.5wt.% or more based on the weight of the negative active material. The maximum charging current is specified to 0.5CA or higher based on a 5 hour rate nominal capacity, and charging electrical capacity is set so as not to exceed discharging electrical capacity. Since charging current is large, charging time is shortened, the formation of a passive film which causes early capacity drop is suppressed, and activity of lead dioxide which is a charging product in a positive electrode is enhanced. By adding carbon to the negative active material, charging efficiency in a negative plate is enhanced, accumulated lead sulfate is activated, and the drop in life is retarded even if large current charging is performed without performing complete charge every discharge.