The response to open-circuit interrupts of porous mixed iron-nickel cathodes operating in NaCl-buffered, molten NaAlCl4 electrolyte has been characterized as a function of state of charge (SOC) for different iron loadings and different charge and discharge rates. After discharge, the open-circuit potential (OCP) can evolve in time from the iron plateau to the nickel plateau, and this behavior can be explained by galvanic interactions between iron metal and Ni2+. Characteristic times of the OCP transients depend on SOC and can be large. When the OCP has converged on a steady state during discharge, its value may provide an estimate of the mole fraction of NiCl2 at the interface of the triclinic (Ni,Fe)Cl-2 film that resulted from metal oxidation. Detailed analyses of the experiment require modeling of the galvanic conversion rates, which depend on both charge-transfer and mass-transfer phenomena. (C) The Author(s) 2015. Published by ECS. All rights reserved.