NOVELTY - Testing a lithium-ion secondary battery (10) comprises after the battery is subjected to a charging process, measuring a potential difference A between an outer can (12) or a sealing plate (13) and a negative electrode external terminal (19); and if the potential difference A is greater than or equal to a predetermined prescribed value, determining the battery as a non-defective product.    USE - Method for testing a lithium-ion secondary battery (claimed) used for electric vehicles and hybrid electric vehicles.    ADVANTAGE - The method allows easy detection of the battery in which a short circuit occurs temporarily, when the negative electrode external terminal and the outer can come into contact simultaneously with a manufacturing apparatus during manufacturing of the battery, where a reliable battery can be sorted out with a reduced possibility of corrosion of the outer can due to lithium metal deposited on the inner surface of the outer can.    DETAILED DESCRIPTION - Testing a lithium-ion secondary battery (10) comprises after the battery is subjected to a charging process, measuring a potential difference A between an outer can (12) or a sealing plate (13) and a negative electrode external terminal (19); and if the potential difference A is greater than or equal to a predetermined prescribed value, determining the battery as a non-defective product. The battery comprises an electrode assembly (11) in which a positive electrode plate including a positive electrode mixture containing a positive electrode active material capable of absorption and desorption of lithium ions and a negative electrode plate including a negative electrode mixture containing a negative electrode active material capable of absorption and desorption of lithium ions are stacked, or stacked and wound with a separator, aluminum or aluminum alloy outer can, and aluminum or aluminum alloy sealing plate to which a positive electrode external terminal (17) electrically connected to the positive electrode plate and a negative electrode external terminal electrically connected to the negative electrode plate are attached in an insulated state, the sealing plate being fixed to a mouth portion of the outer can in a sealed state so as to be electrically connected to the outer can, and the electrode assembly being enclosed together with nonaqueous electrolyte in the outer can.    DESCRIPTION OF DRAWING(S) - The drawing is a front view of the battery.    Lithium-ion secondary battery (10)    Electrode assembly (11)    Outer can (12)    Sealing plate (13)    Positive electrode external terminal (17)    Negative electrode external terminal (19)