Method of operating a secondary battery system having first and second tanks for reserving electrolytes

A method of operating a secondary battery system, the secondary battery system including at least one set of first tanks for reserving electrolytes required for a steady operation, at least one set of second tanks for reserving electrolytes required for an emergency operation, and switching means for allowing selective switching between the electrolytes in the first tanks and the electrolytes in the second tanks to circulate the selected electrolytes through a cell, the method comprising:

• reserving electrolytes having a proportion of a quantity of active material produced in a charging reaction to a total quantity of active material of not less than 50% in the second tanks for the emergency operation;
• using the electrolytes in the first tanks to charge and discharge electricity to ensure operation at a rated output during the steady operation;
• switching from using the electrolytes in the first tanks to using the electrolytes in the second tanks during the emergency operation;
• and
• using the electrolytes in the second tanks to charge and discharge electricity to ensure an overload operation at an output in excess of the rated output during the emergency operation.