Ceria-supported platinum synthesized by a novel solution-combustion method results in ionically substituted platinum sites on nanosized ceria crystallites, and is found to be an excellent hydrogen and oxygen recombinant catalyst at room temperature for recovery of water in sealed lead-acid batteries. The use of this catalyst prevents any change in the quantity or concentration of the sulfuric acid electrolyte in the battery during its operation, which is pivotal to enhancing both its performance and life span. The catalyst could be equally advantageous to alkaline storage batteries, and, in particular, in realizing sealed nickel-iron batteries giving them a revived commercial interest.