To strengthen welding strengh between a lead material for battery and a battery case at the time that the lead material is welded into the case by parallel resistance welding method, and stabilize the welding strength.

A strip-like lead material 2 to be weld into a battery case made of nickel or nickel alloy plated steel sheet by parallel resistance welding method has 0.01-0.1 μm of surface mean roughness Ra in a cross direction of a center line and a welding point position A1-A4 in a direction longitudinally of at least the surface to be welded thereof.