Redox flow batteries are a promising electrochemical technology for large-scale stationary energy storage. Continuous macroscopic models address the design and operational challenges required to increase their profitability and energy market penetration. Controlling the battery operating temperature and avoiding cell overheating are two primary ways to ensure optimal overall efficiency. This work presents a nonisothermal two-dimensional steady-state model of a unit-cell all-vanadium redox flow battery. The model is validated using polarization and open circuit voltage measurements at different temperatures and states of charge. After calibration, a parametric study is used to explore the role of operating temperature on cell performance, deconvoluting the different contributions to cell heating, and providing practical guidance about the thermal effects of operating conditions. The results reveal that increasing the operating temperature improves species mass transfer but negatively affects activation losses; the cell suffers higher overheating during charge than during discharge; and cell length has a proportional effect on cell heating. Lastly, we propose the use of asymmetric electrolyte temperatures as a performance improvement strategy for electrochemical storage systems hybridized with thermal energy storage. The results show that nonisothermal models are a powerful tool for optimizing advanced electrochemical flow reactors in energy storage devices.