Device for supplying an electrolytic solution to a cell of a battery for a plant for the electrochemical formation of batteries, said supply device being susceptible to be removably and sealingly mounted on the cover of a battery at a provided opening of said cover and connected to feeding means and to return means of said plant for the electrochemical formation, characterized in that it comprises: - a tubular body, having preferred extension along a longitudinal direction and comprising one end portion adapted to be at least partially removably inserted in said opening of the cover of said battery, said tubular body also comprising at least one inlet duct susceptible to be connected to said feeding means in order to receive an electrolytic solution flow from the latter and convey it into a corresponding cell of said battery, and an outlet duct susceptible to be connected to said return means for the extraction of said electrolytic solution flow from said cell; - an abutment element fixed to the end portion of said tubular body and having an annular abutment face being extended around said end portion with at least one component thereof substantially perpendicular to said longitudinal direction; - a pressure element mounted on the end portion of said tubular body, and having an annular pressure face facing the abutment face of said abutment element and being extended around said end portion with at least one component thereof substantially perpendicular to said longitudinal direction; - at least one elastically deformable sealing element, which is perimetrically mounted on the end portion of said tubular body, interposed between said annular abutment face and said annular pressure face; said pressure element being movable with respect to said tubular body along said longitudinal direction between a compression position, in which it is brought close to said abutment element and causes the compression of said at least one sealing element along said longitudinal direction and the perimeter expansion thereof via elastic deformation, and a rest position in which it is spaced from said abutment element; - a lever constrained to said tubular body and actuatable to act on said pressure element in order to move it between said rest position and said compression position; said at least one sealing element, elastically deformed due to the action of said pressure element arranged in said compression position, being susceptible to make a seal between said tubular body and the cover of said battery when the end portion of said tubular body is inserted in an opening of said cover. - a tubular body, having preferred extension along a longitudinal direction and comprising one end portion adapted to be at least partially removably inserted in said opening of the cover of said battery, said tubular body also comprising at least one inlet duct susceptible to be connected to said feeding means in order to receive an electrolytic solution flow from the latter and convey it into a corresponding cell of said battery, and an outlet duct susceptible to be connected to said return means for the extraction of said electrolytic solution flow from said cell; - an abutment element fixed to the end portion of said tubular body and having an annular abutment face being extended around said end portion with at least one component thereof substantially perpendicular to said longitudinal direction; - a pressure element mounted on the end portion of said tubular body, and having an annular pressure face facing the abutment face of said abutment element and being extended around said end portion with at least one component thereof substantially perpendicular to said longitudinal direction; - at least one elastically deformable sealing element, which is perimetrically mounted on the end portion of said tubular body, interposed between said annular abutment face and said annular pressure face; said pressure element being movable with respect to said tubular body along said longitudinal direction between a compression position, in which it is brought close to said abutment element and causes the compression of said at least one sealing element along said longitudinal direction and the perimeter expansion thereof via elastic deformation, and a rest position in which it is spaced from said abutment element; - a lever constrained to said tubular body and actuatable to act on said pressure element in order to move it between said rest position and said compression position;