TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The immobilized acid comprises mineral acid that comprises sulfuric acid with specific gravity of 1.05-1.83, preferably 1.25-1.35. The concentration of polymer network is 1-40 wt.%, 2-25 wt.% or 4-12 wt.%. Preferred Components: The polymer network comprises reacted acrylamide, methacrylamide, vinylpyrrolidone, acrylate, methacrylate, resorcinol, bis-acrylamide, N,N'-diallyltartramide, glyoxal or formaldehyde. The polymer network is formed in in water and exchanged into acid. The gel electrolyte further comprises additive that comprises fiber, salt, colloid, soluble or insoluble powder, particulate matter, soluble polymer not integrated into polymer network, silica, alumina, titania, zirconia, glass, wood, cellulose, lignin, lignosulphonate, chitosan, and cross-linked polyvinylpyrrolidone or rubber. The additive is substantially dissolved in the acid and comprises vanillin, zinc sulfate, aluminum sulfate or sodium sulfate. The substrate comprises foam, glass mat, sheet, polymer film, web or membrane. The composite further comprises free acid in some of the pores of the substrate not filled with the gel electrolyte. The positive electrode comprises lead oxide. The negative electrode comprises lead, carbon or activated carbon. The gel electrolyte resists acid stratification and acid spillage. The positive electrode and negative electrode comprise plates and the gel electrolyte is positioned between plates. The positive electrode and negative electrode comprise tubular or spiral shape plate partially surrounded by the gel electrolyte. The polymers comprise linear polyacrylamide, polymethacrylamide, polyacrylate, polymethacrylate or polyvinylpyrrolidone. The monomer, oligomer or polymer precursor comprises acrylamide, methacrylamide, acrylic acid, acrylate, methacrylate, resorcinol or N-vinylpyrrolidone. The cross-linker comprises multi-functional molecule. The reacting step involves free-radical initiation to obtain the covalently cross-linked polymer network. The free-radical initiation is thermally or photo-chemically induced. The electrode is partially covered with the gel electrolyte. The reacting is completed in situ in presence of electrode to cover the electrode with the gel electrolyte. The additive is mixed with the liquid phase and the monomer, oligomer, cross-linker, polymer or polymer precursor before the reacting step.