In order to inhibit sulfation and hydrogen evolution of the negative plates and to prolong the cycle life of valve-regulated lead-acid batteries for hybrid-electric vehicles, electrochemically active carbon (EAC) and Indium (III) oxide (In2O3) are added into negative active materials of valve-regulated lead-acid batteries. The influences of EAC and In2O3 on the cycle performance of valve-regulated lead-acid batteries are investigated under high-rate partial-state-of-charge conditions. Experiment results indicate that addition of EAC in negative active materials can prolong the high-rate partial-state-of-charge cycle performance of valve-regulated lead-acid batteries, whilst it results in the accelerated evolution rate of hydrogen during charge process. It is also observed that EAC with an appropriate amount of In2O3 can effectively increase the overpotential of hydrogen evolution, which can not only produce the decreased hydrogen evolution rate and promote conversion of PbSO4 to Pb in capacity recovery process, but also prolong the high-rate partial-state-of-charge cycle life of valve-regulated lead-acid batteries. The battery added with 0.5% EAC and 0.02% In2O3 in negative active materials exhibits at least four times longer cycle life than that without In2O3. (C) 2012 Elsevier B.V. All rights reserved.