Abstract: Flow battery systems and control methods are disclosed. The flow battery includes components such as positive electrolyte tank, a negative electrolyte tank, a primary stack having a positive porous electrode and a negative porous electrode separated by a membrane, a power bus linked to the electrodes, an electrolyte pump and an auxiliary stack, etc. The power load on a power bus is monitored and as required pumps are activated if the detected power load on the power bus is greater than a first threshold power load. One of the pumps are deactivated if the detected power load on the power bus is less than a second threshold power load which is lower than the first threshold power load.