The feasibility of developing a rechargeable iron ion battery is demonstrated for the first time. A rechargeable iron ion battery using mild steel as the anode and vanadium pentoxide as the cathode is demonstrated to deliver a specific capacity of 207 mA h g-1 at 30 mA g-1. Using ex situ characterisation techniques, reversible intercalation of iron ions into a host structure is confirmed. © 2019 The Royal Society of Chemistry.