Stacking of microfluidic fuel cells and redox batteries may cause internal current losses and reduced performance compared to single cells. In the present work, these internal current losses are investigated experimentally for an array of two microfluidic vanadium redox batteries based on flow-through porous electrodes. A unique cell array design is proposed, having two pairs of flow-through electrodes situated in a single co-laminar flow manifold. The two electrochemical cells are connected electrically in series and have series fluidic connection through the electrolyte in order. to reuse the partially consumed reactants from the first, upstream cell in the second, downstream cell. The cell array prototype demonstrates a maximum power output of 9 mW and a maximum current of 13.5 mA. However, current losses up to 1.75 mA are observed at open circuit, which is attributed to reactant discharge through a parasitic cross-cell comprising of one electrode from each electrochemical cell in the shared manifold. This current loss, appearing in the form of a shunt current, is shown to be proportional to the cell potential. The drop in coulombic efficiency is calculated to quantify the effect of the shunt current. Recommendations for mitigation of shunt current in microfluidic cell arrays are provided. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: [email protected]. All rights reserved.