Rechargeable batteries based on MnO₂/Zn aqueous chemistry have emerged as a viable alternative to Li-ion batteries (LIB), owing to their low material cost, high safety, sustainable redox chemistry, and remarkable electrochemical performance with an energy density comparable to LIBs. However, the reaction mechanism, particularly the detailed electrochemical process that leads to MnO₂ deposition during the charge process, remains elusive to date despite a decade of intensive research. In this study, we utilized various structural analysis methods, including in situ Raman spectroscopy, on simulated discharged electrodes to demonstrate that the charging reaction consists of two reaction steps. These steps involve the precipitation of highly defective phyllomanganates with heavy Zn sorption in the interlayer, followed by the coincidental extraction of zinc and incorporation of manganese into vacancies in MnO₆ sheets, which lead to the production of phyllomanganates with much reduced Zn content. This study sheds light on the reaction mechanism of MnO₂/Zn batteries and opens new opportunities for improving their performance to commercial levels.