Studies have shown that the different vanadium ions in the all-vanadium redox battery (VRB) exhibit unequal rates of diffusion across the ion exchange membrane that gives rise to capacity loss due to a build up of vanadium ions in one half-cell with a corresponding decrease in the other. In this paper concentration profiles of the different vanadium ions have been modeled as a function of time under different charge and discharge currents in order to predict expected capacity loss over extended charge-discharge cycling. In the case of cation exchange membranes, a build up in total vanadium ion concentration in the positive half-cell is predicted, in agreement with observed trends in laboratory prototype VRB systems. Effects of factors other than diffusion are discussed in detail, along with electrolyte maintenance strategies to restore capacity during long-term VRB operation. (c) 2012 Elsevier B.V. All rights reserved.