Rechargeable aqueous batteries are highly desirable for large scale energy storage due to their low cost and high safety. Lead acid batteries are low cost aqueous systems and much easy to scale up for stationary applications. Nevertheless the use of lead causes significant environmental concern besides the low energy density and limited life span, even though lead-acid batteries still account for more than half of the global battery market. An alternative, low cost and high safety aqueous energy storage system is highly desirable. Herein, we demonstrated a highly reversible chemical conversion reaction mechanism of Zn/MnO₂ systems in optimized mild aqueous electrolytes. This conversion reaction provides an operating voltage of 1.44 V, high capacity of 285 mAh g^-1 (MnO₂), excellent rate, and capacity retention of 92% over 5000 cycles. Zn metal anode also shows high reversibility. The highly reversible and stable chemistry in aqueous Zn/MnO₂ batteries opens new opportunities and can be a viable alternate to the widely used lead acid batteries.