NOVELTY - The vanadium based redox flow cell system battery comprises a stack (102) of flow cells (146), electrolyte storage tanks coupled to provide electrolyte to the stack and to receive electrolyte from the stack, and a rebalance system coupled to adjust the electrolyte stored in the electrolyte storage tanks. The rebalance system introduces: a reducing agent to the electrolyte to correct a positive imbalance; and oxidation to correct a negative imbalance or an oxidizing agent to the electrolyte to correct the negative imbalance. The rebalance system includes an air pump.    USE - Used as a vanadium based redox flow cell system battery.    ADVANTAGE - The economically feasible vanadium based redox flow cell system battery has improved performance and high energy density.    DETAILED DESCRIPTION - The vanadium based redox flow cell system battery comprises a stack (102) of flow cells (146), electrolyte storage tanks coupled to provide electrolyte to the stack and to receive electrolyte from the stack, and a rebalance system coupled to adjust the electrolyte stored in the electrolyte storage tanks. The rebalance system introduces: a reducing agent to the electrolyte to correct a positive imbalance; and oxidation to correct a negative imbalance or an oxidizing agent to the electrolyte to correct the negative imbalance. The rebalance system includes an air pump coupled to an injector tube, a Venturi pump, and a valve coupled to an injector tube. The electrolyte having V4+/V5+ are exchanged with electrolyte having V2+/V3+ to correct the positive imbalance. The electrolyte having V2+/V3+ are exchanged with electrolyte having V4+/V5+ to correct the negative imbalance. The rebalance system is controlled by a controller and integrated into a firmware. INDEPENDENT CLAIMS are included for:    (1) a method of rebalancing a positive imbalance in a flow cell system; and    (2) a method of rebalancing a negative imbalance in a flow cell system.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a flow cell system.    Stack (102)    Pipes (108)    Cooling fans (138)    Control system (142)    Flow cells. (146)