Electrochemical energy storage utilising batteries is a viable option for storing electrical energy in diverse applications. Amongst different chemistries, lithium is a well-deployed chemistry for electrochemical energy storage, given its high unit cell voltage and energy density. However, alternate chemistries to lithium are explored due to the discrepancies in lithium- centric technology developments. Such alternate batteries should be energy efficient to be used in any potential energy storage application. To improve the performance of any battery with a pre-defined cell architecture, parametric optimisation is essential. In this study, we selected two batteries, vanadium redox flow battery (VRFB) and zinc-air flow battery (ZAFB), which have been explored widely as a potential replacement for lithium in electric vehicles and renewable energy storage applications. A comprehensive literature study on VRFB and ZAFB helped us to determine the major research gap, which is the absence of parametric optimisation of all the physical and chemical parameters simultaneously. When we looked at the current positions of the chosen batteries, VRFB had a good amount of literature data and close to 14 parameters, whereas ZAFB had less literature data and only 6 parameters. Hence, for VRFB, we decided to go with a data-driven modelling approach, given the sufficient literature data and many parameters. For ZAFB, we decided to go with an all-experimental approach, given less literature data and fewer parameters. A data-driven VRFB model that was 90 % accurate in predicting energy efficiency with a difference of less than ±2 % was built and used to determine the optimised parametric setting to achieve maximum energy efficiency. According to this study, a VRFB cell with base + thermal treated felt, 70 % felt compression, interdigitated flow field, an AIEM membrane, and 1-butyl-3 methylimidazolium chloride as an electrolyte additive can achieve a maximum energy efficiency of 97 - 98 % at a current density of 50 mA cm-2. Similarly, for ZAFB, the all-experimental approach for parametric optimisation revealed that a ZAFB cell with KOH polymer gel electrolyte as separator and MnO2 as oxygen reduction reaction catalyst showed a maximum nominal voltage of 1.23 V at the optimised parametric setting with a high electrolyte flow rate of 100 mL min-1, low electrolyte volume of 100 mL, high electrolyte concentration of 7 M, and electrolyte temperature of 40 °C. The parametric optimisation approaches followed in this research study can be adopted for optimising the parameters in other emerging batteries.