Liquid metal batteries (LMBs) comprising electrodes of two different liquid metal alloys separated by a molten salt electrolyte have been shown to be high rate-capability energy storage devices. In an effort to specify the limits of the LMB performance envelope, i.e., the electrical output of the cell, the charge transfer kinetics at the positive electrodes in Li-Bi and Mg-Sb have been characterized by electroanalytical methods. The variation in exchange current density, j(0), with depth of discharge yielded average values of 60 A/cm(2) in Li-Bi and 12 A/cm(2) for Mg-Sb. These values confirm the highly facile nature of the liquid-liquid metal-salt interface and indicate that the current in these cells is not limited by electron transfer. (C) The Author(s) 2017. Published by ECS. All rights reserved.