SURFACE-TREATED STEEL SHEET FOR BATTERY CASES, BATTERY CASE, AND BATTERY

A surface-treated steel sheet for battery cases is provided which comprises a nickel-cobalt alloy layer formed at the outermost surface of a plane to be an inner surface of a battery case, wherein a Co/Ni value at the surface of the nickel-cobalt alloy layer is within a range of 0.1 to 1.5 as determined by Auger electron spectroscopy analysis.