Studies have shown that the temperature of the electrolyte solutions in the vanadium redox flow battery (VFB) has a significant impact on the battery performance. In this paper, a thermal model for the VFB has been developed on the basis of the conservation of energy to predict the battery temperature as a function of time under different operating conditions and structure designs. Simulations of battery and electrolyte temperature at both constant and varying environmental temperatures show that the presenting model is able to effectively forecast the fluctuation of the battery temperature in the presence of different charge and discharge currents. As expected, increasing current or reduced flow rate will increase the stack and electrolyte temperature. Thermal properties of the tank material and its surface area can however be adjusted to optimize heat transfer to the atmosphere to reduce overheating. This model can be employed to develop a model-based control system which will manage the electrolyte temperature in the optimal range. Further possible improvements to the model are also discussed.