NOVELTY - The water replenishment plug for batteries, comprises a valve, which limits the replenishment of distilled water when the desired acid filling level is reached and has a float (3), which is immersed in the battery acid, where the surfaces of the float are provided with a coating or treatment, which has a self-cleaning effect and a dirt-repellent effect. Transmission parts (4) are equipped between the float and valve sealing body (2) externally with the self-cleaning and dirt-repellent coating or treatment.    USE - Water replenishment plug useful for batteries (claimed).    ADVANTAGE - The water replenishment plug has improved heat resistance and self-cleaning- and dirt-repellent effect.    DETAILED DESCRIPTION - The water replenishment plug for batteries, comprises a valve, which limits the replenishment of distilled water when the desired acid filling level is reached and has a float (3), which is immersed in the battery acid, where the surfaces of the float are provided with a coating or treatment, which has a self-cleaning effect and a dirt-repellent effect. Transmission parts (4) are equipped between the float and valve sealing body (2) externally with the self-cleaning and dirt-repellent coating or treatment. The valve sealing body, valve seat (6) and/or guidance of the float is provided with the self-cleaning and dirt-repellent coating or treatment. The self-cleaning and dirt-repellent coating or treatment has a surface, which has a nano-structure and is hydrophobic. The particles of the coating surface consist of hydrophobic silicic acid, zinc oxide and/or titanium dioxide. The particle has average diameter of 0.02-100 mu m. The surface has elevations of 5-200 mu m and the height of the elevation is 5-100 mu m. The elevation consists of hydrophobic polymers or durable hydrophobic materials and the elevations are not detachable by water or water containing detergents. The coating or surface treatment is carried out with plasma.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a water replenishment plug.    Valve sealing body (2)    Float (3)    Transmission part (4)    Valve rod (5)    Valve seat. (6)