In a zinc-persulfate battery, active metal-zinc pieces were used as an anode and ammonium chloride as an electrolyte in an anode zone, with soluble oxidants-persulfate as an active cathode substance and electrolyte in the cathode zone. Carbon felt was used as an inert cathode, with a PE-01 homogeneous membrane between the anode and cathode zones as well as 100 mL of solution in both the anode and cathode zones. The discharge characteristics of the battery at 5 Omega was investigated for various temperatures and concentrations of ammonium persulfate, sodium persulfate, and ammonium chloride, and a flat discharge characteristic was obtained. The output energy of the zinc-persulfate battery increases remarkably on increasing the concentrations of persulfate and ammonium chloride, as well as temperature. The output energy of the zinc-sodium persulfate battery is greater than that of a zinc-ammonium persulfate battery. If the concentration of ammonium persulfate is less than or equal to 1.25 M, crystals did not form in the cathode zone after discharge when the temperature was above 0 degrees C. Crystals formed are a mixture of (NH4)(2)Zn(SO4)(2)center dot 6H(2)O, (NH4)(2)Zn(SO4)(2), (NH4)(2)SO4, and (NH4)(3)H(SO4)(2). (NH4)(2)Zn(SO4)(2) is the major constituent, and the others are the minor ones. The maximal and least actual gravimetric energy densities of the Zn-(NH4)(2)S2O8 battery are 48.15 and 20.78 W h kg(-1), respectively.