Abstract: A plant for the forming of lead-acid battery cells includes plugs to be fitted to the openings of the cells, each plug including a first inlet duct, a second outlet duct to set up a circulation of electrolyte inside the cell and supply and balancing elements to dilute with air the inflammable gases formed in the cell and to favor the balancing of the pressure inside the cell with the external atmospheric pressure. The supply and balancing elements include a third supply and balancing duct connecting the upper part of the plug with a part of the supply tank at atmospheric pressure which introduces the electrolyte into the cell. The plant includes a fan which forms a vacuum in the suction header, drawing the electrolyte and the inflammable gases from the cells and, through the third duct, ventilating the cells without forming a vacuum inside them.