 Pressed-plate carbonyl iron electrodes for rechargeable iron–air batteries have recently been described to undergo a considerable electrochemical formation before they attain a stable and competitive discharge capacity in concentrated alkaline electrolyte. In this study, the impact of the charging conditions on the discharge performance due to electrochemical formation was investigated. Based on the results, it is demonstrated that the preset charge capacity mainly determines the resulting discharge capacities of the porous electrodes in the steady state at the end of the formation period. Furthermore, the present study elucidates the electrode processes behind formation and expands the existing phenomenological model that has recently been established to explain the evolution of the discharge capacity. Finally, feasible criteria for the comparison of different anode architectures are discussed.