TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Parameters: The electric current generated by the ionic communication between anode and cathode yields a battery voltage of greater than or equal to 0.9 V, preferably 0.9-3 V. The liquid-activated battery is flexible.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The anode contains anode material consisting of zinc, magnesium, aluminum, calcium, lithium, conducting polymers, iron, nickel, and/or metal oxides. The cathode contains cathode material consisting of copper, carbon, silver, metal oxides, conducting polymers, carbon, carbon nanotubes, graphite, and/or graphene. The electrolyte is salt, acid, and/or base. The salt is ammonium sulfate, ammonium hydrogen sulfate, ammonium nitrate, ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium chloride, sodium hydrogen sulfate, potassium hydrogen sulfate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, potassium phosphate, sodium carbonate, and/or potassium carbonate. The acid is citric acid, glutaric acid, lactic acid, boric acid, acetic acid, propionic acid, phosphoric acid, phosphorous acid, hydrochloric acid, sulfuric acid, amino acids, and/or sulfonic acids. The base is sodium hydroxide, potassium hydroxide, calcium hydroxide, and/or lithium hydroxide. The hydrophilic polymer contains (pHEMA), the anode contains zinc, the cathode contains copper, and the electrolyte contains ammonium chloride. The liquid is water e.g. ground water, industrial water effluent, drinking water, rain water, brackish water, surface water, mineral water, salt water, substantially fresh water, distilled water, and/or deionized water. The battery contains a salt operative to reduce corrosion of anode. The salt contains zinc chloride.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The hydrophilic polymer is polymethacrylate, polyacrylate, polymethacrylamide, polyacrylamide, polyvinyl alcohol, polyvinyl acetate, (modified) cellulose, (modified) collagen, (modified) polysaccharide, polynucleotide, and/or polyelectrolyte, preferably polyhydroxyethyl methacrylate (pHEMA). The polymerization initiator contains 2,2'-azobis-2-methyl-propanimidamide dihydrochloride (AAPH). Preferred Processes: The hydrogel is prepared by combining greater than or equal to 1 hydrophilic polymer, greater than or equal to 1 polymerization initiator, and greater than or equal to 1 electrolyte in a mold, and the anode and the cathode are arranged to be in contact with the hydrogel by inserting the anode and the cathode into the mold in contact with the hydrogel such that the anode does not contact the cathode. The contents of the mold are cured by heating the mold in oxygen-free oven, dried in forced air oven, removed from the mold, and housed in a battery case configured to allow entry of liquid.