Metal-air (O2) batteries, owing to their high theoretical energy densities in comparison to metal ion batteries, are emerging as potential plausible energy storage solutions. Out of different metals (Li, Zn, Al, Fe etc.) based rechargeable metal-air battery systems, Zn based energy storage systems find a niche and are considered for futuristic applications as secondary battery due to safety, cost efficiency, widespread abundance, and environmental compatibility along with higher energy density. Apart from the higher safety aspects of metallic Zn, the use of aqueous electrolytesalkaline or neutral, in the system brings additional safety feature to the Znair battery (ZAB) unlike that in the Li-air batteries. ZABs are the potentially proven metal-air battery systems in small scale energy storage to grid level storage, and their primary batteries are largely being used in hearing aids. It holds strong promise for future electric vehicles as well as in mini power grids to store intermittent renewable energy. Despite the merits, commercial development of ZAB systems still remains a bottleneck due to some of the following issues: (a) challenges in the development of a bifunctional electrocatalyst for cathode to facilitate the oxygen evolution reaction (OER, during the charging of the battery) and oxygen reduction reaction (ORR, during the discharge of the battery), (b) early passivation of Zn anode due to thick ZnO formation causing cell death,(12) (c) parasitic reactions leading to low coulombic efficiency, self-discharge, and cell malfunctioning. Significant progress has been made during the past few years on the development of bifunctional electrocatalysts for ORR and OER, leading towards the realization of low-cost, durable porous cathodes . In the anodic side (Zn), early ZnO passivation, dead dendrite formation, and parasitic chemical reactions are identified as the critical issues to be addressed. The strategies such as electrolyte modification, electrode structure engineering, anode composition modification, deployment of solid-state electrolyte etc. have been suggested as the solutions to address the early cell death, low columbic efficiency, and self-discharge. Although the sluggish cathodic kinetics is known to play the rate limiting role in a ZAB, however at higher current densities, both anodic and cathodic processes determine the cell life of ZAB. In an alkaline ZAB, metallic Zn is in contact with alkaline electrolyte, and it can lead to a chemical reaction forming H2. This inevitable process leads to the corrosion of Zn and reduction in the columbic efficiency of a conventional ZAB. Similarly other side reactions such as, the role of purity of air supplied at the cathode has also been investigated. It was shown that CO2 in the air can affect the battery performance due to the formation of soluble and insoluble carbonate and bicarbonate ions.(26) However, O2 in the air is the reactant supplied at the cathodic side of a ZAB (fuel for the ORR process) and it is soluble (10 -3 -10 -4 mol/L) in alkaline solution. Limiting the amount of O2 at the cathode leads to a higher over potential in the battery discharging process and hence O2 mass transfer is critical at cathode (as proven in the later part). Herein we probe the influence of O2 (g) or dissolved O2 on the anodic side of a ZAB or Zn-O2 battery, revealing the possibilities of parasitic reactions other than the well explored hydrogen evolution reaction (HER).