Discharging products at the positive electrode of a rechargeable Zn/ZnSO4(aq)/ gamma-MnO2 cell have been identified. ZnSO4.3Zn (OH)(2).5H(2)O is produced at the positive electrode as proved by X-ray diffractometry. Mn3O4 is identified as the main manganese product by both X-ray diffractometry and chemical treatment of the discharging product with dilute H2SO4 followed by analysis of the Zn:Mn ratio in the discharging product. The charging and discharging behavior of other Zn/ZnSO4(aq)/MnO2 cells have been examined by using several known types of MnO2 as well as newly prepared MnO2. Thus "new type manganese oxide" and "amorphous oxide" have been prepared by treatment of K2Mn4O8 and Mn3O4 respectively with dilute H2SO4, and "new type manganese oxide" is assumed to have an Mn-O framework similar to that of K2Mn4O8. Investigation of the discharging behavior and rechargeability of various Zn/ZnSO4(aq)/MnOx cells using various manganese oxides reveals that manganese oxides with relatively large spaces (hole, tunnel, layer and amorphous spaces as in cases of gamma-, alpha- and delta-MnO2, "new type manganese oxide" and "amorphous manganese oxide") show good discharging behavior and rechargeability. However, manganese oxide or gamma-MnOOH with smaller hole or tunnel structures (beta- and lambda-MnO2 and gamma-MnOOH) is neither active in the primary cell nor rechargeable.