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In the science and technology of electrochemical energy storage, different allotropes of MnO2, fabricated with a variety of methods, are assembled into electrodes, playing the role of cathode or oxygen reduction reaction (ORR) electrocatalyst. Often, MnO2‐based cathodes are combined with Zn anodes into different types of batteries, resulting in contact between MnO2and its electrochemical reaction products, and Zn2+. Awareness is growing that this interaction adversely affects the functional performance of MnO2, but no definitive understanding has been reached for this issue. This study contributes, through electrochemical measurements accompanied by microscopy and Raman spectroscopy, to a better understanding of the way the electrochemical behavior of two technologically representative types of manganese dioxide ‐ hydrothermally grown α‐MnO2and electrodeposited γ‐MnO2(EDM) ‐ is degraded when these materials are exposed to neutral and alkaline aqueous solutions, containing Zn2+. Specifically, we highlighted different types of irreversible changes in electrochemical response, which can be interpreted with phase‐formation processes. Such changes result in the deactivation of α‐MnO2as ORR electrocatalyst, and of both α‐MnO2and EDM as zinc‐ion battery (ZIB) cathodes. The electroactivity of EDM for ZIB operation can be restored if Mn2+is added to the neutral electrolyte, because a phase, active in discharge, is electrodeposited during charging. In alkaline and neutral aqueous solutions, Zn2+interacts with hydrothermally grown α‐MnO2nanorods and electrodeposited manganese dioxide films, causing irreversible degradation of oxygen reduction reaction (ORR) and Zn2+‐intercalation performances. Degradation results from the formation of mixed Zn/Mn oxides and Zn2+‐containing basic salt layers. ORR stability mandates the elimination of contact of MnO2with Zn2+, while zinc‐ion battery cyclability is enabled by electrodepositing fresh ZnMn2O4in the recharge period.