Aqueous energy storage systems provide complex and unique challenges due to electrolyte and material instability in the realistic potential window of interest. The inherent intrigue of aqueous systems is the safe, low-cost, environmentally friendly nature of the electrolyte. In the interest of using low-cost, non-toxic materials, we studied the evolution of manganese oxide in aqueous zinc-ion batteries, highlighting and utilizing its instability. Aqueous zinc-ion batteries in near neutral electrolyte were initially developed as an analogy to the rocking chair Li-ion battery, targeting employment of a Zn-intercalation mechanism at the cathode. However, the nature of the aqueous system means that other effects such as Mn-dissolution, proton-intercalation, water electrolysis, and the effect of pH must be considered. A combination of materials and electrochemical characterization reveals the dominant challenge in this system to be the irreversible phase changes of manganese oxide and concurrent Mn-dissolution. We find that the electrolyte has a major influence on the trajectory of the cathode material. Ultimately, we transform the instability of the electrochemical interface from an obstacle into an advantage and reveal the potential for batteries to leverage a dynamic interface.