To all the experts on the subject "Get it, it's a magnet, it can't be nickel": Nickel is magnetic! If you want to know if a nickel-plated strip is galvanized steel, hold a grinder on it to reveal the cross-section and soak it in a saturated seawater bath overnight. This spot welding goes well with a LiPo spot welder, probably fits up to about 6A with a single strip.