A lithium-ion battery system includes: a lithium-ion battery including a cathode and an anode, the cathode containing a lithium manganese-nickel complex oxide as a cathode active material, and the anode containing a lithium-titanium complex oxide as an anode active material; and a charge regulation means which regulates an end-of-charge voltage Vf within a range of 3.6 V≤Vf≤4.0 V.