Vanadium redox flow batteries (VRFBs) are widely used in various stationary applications to enhance power management, improve peak shaving and load leveling, and support a renewable power grid. Although a VRFB has several advantages such as flexibility, long shelf life, and relatively high efficiency, there are very few commercially available VRFB systems because of high operating and structure costs. Therefore, considerable efforts are being made to reduce the fixed and variable costs of a VRFB system. For effective handling of the VRFB system, it is essential to understand the operational problems that could occur during a long-term VRFB operation. Electrolyte imbalance is often a major obstacle affecting the battery capacity loss. This paper presents a comprehensive reviews on causes, effects, measurement, and regeneration of the imbalanced electrolyte leading to an understanding for better operation and to manufacture a VRFB commercial system. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.