In a method of reflow soldering, a non-aqueous electrolyte secondary battery is discharged to a first discharge voltage different from a second discharge voltage at an inflection point in a discharge curve of the non-aqueous electrolyte secondary battery having an axis of abscissa representing discharge capacity and an axis of ordinate representing discharge voltage. The discharged non-aqueous electrolyte secondary battery is placed on a substrate which is then exposed to a reflow soldering temperature to reflow solder the non-aqueous secondary battery to the substrate. The first discharge voltage is higher than the second discharge voltage to prevent degradation of characteristics of the non-aqueous electrolyte secondary battery resulting from decomposition of the non-aqueous electrolyte due to reaction of the non-aqueous electrolyte with excessive lithium ions in the cathode active material when the non-aqueous electrolyte secondary battery is exposed to the reflow soldering temperature.