Abstract: A device that serves to automatically fill battery cells with water includes a filler plug that can be placed in the cell. The plug has two connection members for the water supply as well as a valve operated by a float. The valve body is connected in articulated fashion to the float, which is arranged centrally in the plug housing, via a pivotally mounted amplifying lever. Between the valve with the valve body and the connection member there is a substantially vertical overflow wall with a free upper edge that is higher than the horizontal upper edge of the bore of the connection members so that a U-shaped feed duct is formed that leads to the overflow wall.