Ever increasing acceptance of electric vehicles relies on better operation and control of large battery packs. The individual modules in large battery packs cannot have identical characteristics and may degrade differently due to manufacturing variability and other factors. Degraded battery modules waste more power, affecting the performance and economy for the whole battery pack. Also, such impact varies with different trip patterns. It is beneficial if the performance gain can be evaluated online prior to replacing certain battery module regarding to actual driving. In this paper, the research objectives are two-fold. First, we propose an on-line battery module degradation diagnostic scheme using the intrinsic signals of battery module equalization. Without need for additional sensors or offline tests, this scheme is cost-effective for constructing and updating the battery pack “health map” in real time during the vehicle operation. Secondly, based on the derived battery health map, the Worthiness of Replacement (WOR) for certain modules/cells is proposed to evaluate the performance of the battery pack for customer specified trip. Such evaluation index provides a quantitative measure for module replacement and battery pack swapping Simulation study is performed to validate the proposed ideas using an actual driving cycle recorded for a commuting trip.