Globally, the supply of electric vehicles is rapidly increasing due to the regulation of CO₂ emission. Laser welding is essential for core parts of electric vehicles, and welding of copper (Cu) material accounts for a large proportion. Unstable welding quality can cause fire and threaten the life of the operator. Quality is urgently needed. In-depth research on Cu sheet laser welding is needed. Laser welding for electric vehicle battery uses a lot of copper. However, IR laser is difficult to achieve stable melting and quality control due to the high reflectivity of copper, and the beam penetrates the battery, causing cell damage and fire. In this study, core parts such as cylindrical batteries of electric vehicles are welded using a green laser for stable fusion and quality. In this study, a 2 kW green laser welding system and a 6-axis industrial robot were used. Green laser welding process technology is applied using nickel-coated 0.5 mm copper on the top and 0.5 mm mild steel on the bottom. Optical microscope analysis was used to examine the penetration after green laser welding.  The laser welding microstructural modification was investigated using scanning electron microscope(SEM) and energy disperse X-ray spectrometer(EDS). After green laser welding, the result is measured using shear stress test. Moerever, Using Laser welding monitoring system(LWM) the causes of welding defects were identified and the process conditions for welding quality deterioration were matched.