With the rapid development of the new energy vehicle (NEV) industry, standardization of battery fault diagnosis and after-sales services has become crucial for ensuring vehicle safety and enhancing user experience. This study explores five dimensions: battery fault types, diagnostic technologies, standardized design of after-sales processes, quality management systems, and practical case studies. It proposes a multi-dimensional data fusion-based fault diagnosis model and a full-process standardized service solution, providing theoretical support and practical references for the industry.