A battery assembly disclosed herein is a battery assembly before being subjected to initial charge. In the battery assembly, a positive electrode has a positive electrode mixture layer that contains a positive electrode active material and NMP, and an oxalate complex compound and FSO3Li are contained in a nonaqueous electrolyte solution. In the battery assembly disclosed herein, a NMP content in the positive electrode mixture layer is 50 ppm to 1500 ppm, the DBP oil absorption of the positive electrode active material is 30 ml/100 g to 45 ml/100 g, and a FSO3Li content in the nonaqueous electrolyte solution is 0.1 wt % to 1.0 wt %. With this, it is possible to prevent a reduction in input-output characteristics caused by formation of a film derived from NMP on the surface of the positive electrode active material, and hence it is possible to prevent an increase in facility cost and a reduction in manufacturing efficiency caused by adjustment of the content of NMP.