Poor cycling stability and mechanistic controversies have hindered the wider application of rechargeable aqueous Zn–MnO₂ batteries. Herein, direct evidence was provided of the importance of Mn²⁺ in this type of battery by using a bespoke cell. Without pre‐addition of Mn²⁺, the cell exhibited an abnormal discharge–charge profile, meaning it functioned as a primary battery. By adjusting the Mn²⁺ content in the electrolyte, the cell recovered its charging ability through electrodeposition of MnO₂. Additionally, a dynamic pH variation was observed during the discharge–charge process, with a precipitation of Zn₄(OH)₆(SO₄)⋅5H₂O buffering the pH of the electrolyte. Contrary to the conventional Zn²⁺ intercalation mechanism, MnO₂ was first converted into MnOOH, which reverted to MnO₂ through disproportionation, resulting in the dissolution of Mn²⁺. The charging process occurred by the electrodeposition of MnO₂, thus improving the reversibility through the availability of Mn²⁺ ions in the solution.