PURPOSE: To increase performance by increasing initial charge efficiency of a lead-acid storage battery by simple procedure.

CONSTITUTION: An electrolyte having a specific gravity of 1.180∼1.225 is poured in a lead-acid storage battery assembled by using an electrode which is not formed so that the electrolyte has a specified specific gravity of 1.240∼1.280 during charge or in completion of initial charge. After the electrolyte is poured, the lead-acid storage battery is allowed to stand for a specified time to make the electrolyte penetrate sufficiently in the electrode. Then, for example, a constant initial charge current obtained by dividing initial charge capacity, which is 270∼320% of theoretical charge capacity of a cathode plate in the lead-acid storage battery by initial charge hours, 40∼45hr, is passed. When initial charge capacity of the lead-acid storage battery reaches 100% of theoretical initial charge capacity of an anode plate, and an electrolyte temperature reaches 50°C or more, the lead acid storage battery is cooled with air blast passed through a cooling water shower, and when electrolyte temperature is down to 50°C or less, air blast is stopped.