Improved plant for the electrochemical formation of lead-acid batteries, which comprises a circuit for circulating the electrolytic solution for the purpose of controlling its temperature and electrolytic concentration, provided with supply means for conveying into the cells via a first distribution header a first flow of electrolytic solution at a constant piezometric pressure and return means for removing under a vacuum by means of a suction header the first flow of electrolytic solution from the cells. A cap, which comprises an inlet pipe connected via a first connecting line to the first distribution header and an outlet pipe, is removably mounted in a sealed manner on each cell. Each cap also comprises at least one ventilation pipe which connects the internal environment of the cell, present underneath the lid, to the external environment which is at atmospheric pressure, so as to dilute the formation of inflammable gases inside said cell.