Provided are a battery and a lead member, designed so that high strength of weld between them can be maintained with less variation despite the supply of lower welding current thereto when the lead member is welded to the outer surface of the battery by the parallel resistance welding method, and a battery pack using the same. A layer of an Ni-based alloy, e.g., an Ni—Fe alloy, is formed on a part or the whole of the outer surface of the battery. The lead member for battery connection is composed of a substrate and an Ni—Sn alloy layer formed on that surface of the substrate which is welded to the outer surface of the battery. The battery pack is composed of a battery group that is assembled by using the battery and/or the lead member and stored in a shell.