Electrochemical devices integrating a fuel cell with a hydrogen storage medium are able to function as secondary batteries. Batteries incorporating a partially oxygenated carbon anode with a RuO2/C cathode exhibit excellent reversibility, but their performance is not yet sufficient for secondary battery applications. This is due to excessive oxygenation of the anode, degradation of the cathode and the excess weight of the electrolyte membrane. In the present work, we addressed these challenges through various improvements in the design of a rechargeable proton-exchange membrane battery. These included coating the surface of a significantly oxygenated carbon anode (O/C atomic ratio 0.131) with carbon black nanoparticles, nanocrystallization of a carbon-free RuO2 cathode (avg. crystallite size 1.1 nm) and the synthesis of an inorganic-organic composite electrolyte membrane. As a result of these optimizations, coulombic efficiencies of over 95% were achieved during charge/discharge over the voltage range of 0.0-1.5 V at 75 degrees C. The resulting device exhibited an initial capacity of 330 mAh g(-1) and was stable over 300 cycles, with maximum energy and power densities of 47 Wh kg(-1) and 1114 W kg(-1), respectively (C) The Author(s) 2016. Published by ECS. All rights reserved.