[Problem] To provide a means that makes it possible to reduce error when displaying the state of charge of a nonaqueous-electrolyte secondary battery that uses a spinel-type lithium/manganese composite oxide as a positive-electrode active material and in particular is expected to be used in high-output situations (has a low internal resistance of 10 m[omega]/Ah (at a SOC of 50%) or less), even if there is a temporary drop in cell voltage due to use with a high-output load or the like. [Solution] This nonaqueous-electrolyte secondary battery has an internal resistance of 10 m[omega]/Ah or less (at a SOC of 50%) and has an electricity-generating element containing the following: a positive electrode obtained by forming, on the surface of a positive-electrode collector, a positive-electrode active-material layer containing a positive-electrode active material; a negative electrode obtained by forming, on the surface of a negative-electrode collector, a negative-electrode active-material layer containing a negative-electrode active material; and a separator. The positive-electrode active material is made to contain a spinel-type lithium/manganese composite oxide and a lithium/nickel composite oxide, with the lithium/nickel composite oxide constituting 50-70% of the combined weight of the spinel-type manganese positive-electrode material and the lithium/nickel composite oxide.