An ASPEN Plus based model is presented for an intermediate-temperature solid oxide iron–air redox battery (IT-SOIARB) system. The model shows that the energy efficiency of the system can be as high as 83%. Furthermore, the model is used to determine the factors that affect the energy efficiency of the battery. With air as the working fluid, a heat exchanger and thermal storage unit are included in the battery system to utilize effectively the heat generated from the discharge cycle in the charge cycle. The results show that air utilization (or air mass flow rate) plays a key role in regulating heat flow between the battery components.