As renewable energy production has become more popular in society, the need for large scale energy storage has increased. By storing energy from sources such as solar and wind power, energy can be produced when it is most feasible and dispatched when there is demand. Such infrastructure would significantly increase the viability of renewable energy technologies. Zinc-air batteries are a promising type of energy storage system which has the potential to solve the grid energy storage problem. A thermo-electrochemical model was developed to provide an order-of-magnitude approximation of the performance of a novel zinc-air battery which has separate charge and discharge stacks coupled with a large fuel storage reservoir. This configuration enables independent scaling of system discharge output power, charge speed, and energy capacity. Because of this flexibility, the system could be tailored to various projects as needed where there may be more importance on some performance characteristics over others. The model was validated using a reference case where the results were evaluated. The capabilities of the model were discussed, including the advantages and disadvantages. The model performs well for order-of-magnitude level approximations of system performance, and opportunities to refine the model in the future were suggested.