A storage battery system includes a battery module A with a first nonaqueous electrolyte battery including a negative-electrode material which has an average grain size of 2 μm or more and is used to occlude and discharge lithium ions, a battery module B with a second nonaqueous electrolyte battery set at a lithium-ion-occluding potential of 0.4V (vs.Li/Li) or more, and including a negative-electrode material which has an average grain size of primary particles of 1 μm or less and is used to occlude lithium ions, and a controller configured to intermittently connect the module A to the module B to intermittently supply power from the module A to the module B to set a charge state and a discharge depth of the second nonaqueous electrolyte battery within a range of 10 to 90%, when no power is supplied to the module B at least from an outside.