Apparatus for filling the case (20) of a lead battery of the open type or of the sealed type with gas recombination, the case being filled with components for forming a gelled electrolyte, and the apparatus being characterized in that it comprises: at least two tanks (1, 2) containing said components, the first tank (1) containing sulfuric acid and the second tank (2) containing a mixture of water and a gelling agent such as particles of silica; at least two receptacles (4, 5) each connected to a respective one of the tanks (1, 2) and each containing a piston (10, 11) for expelling said components from said receptacles into pipes (17, 18); a mixer (16) into which said pipes (17, 18) open out; and a pipe (19) connecting said mixer (16) to the case (20) of said battery through the lid (21) of said battery.