For an operating flow battery system, how the battery's performance varies with ambient temperatures is of practical interest. To gain an understanding of the general thermal behavior of vanadium redox flow batteries (VRFBs), we devised and tested a laboratory-scale single VRFB by varying the operating temperature. The voltage efficiency of the VRFB is found to increase from 86.5% to 90.5% at 40 mA/cm(2) when the operating temperature is increased from 15 degrees C to 55 degrees C. The peak discharge power density is also observed to increase from 259.5 mW/cm(2) to 349.8 mW/cm(2) at the same temperature increment. The temperature increase, however, leads to a slight decrease in the coulombic efficiency from 96.2% to 93.7% at the same temperature increments. In addition, the capacity degradation rate is found to be higher at higher temperatures. (C) 2015 Elsevier Ltd. All rights reserved.