Ever increasing acceptance of electric vehicles relies on better operation and control of large battery packs. The individual cells in the large battery packs cannot have identical characteristics and may degrade differently due to its manufacturing variability and other factors. It is beneficial to evaluate the performance gain by replacing certain battery modules/cells during actual driving. We have a two-fold objective for this research. First, we are developing an on-line battery module degradation diagnostic scheme using the intrinsic signals of a battery pack equalization circuit. Therefore, a battery “health map” can be constructed and updated in real time. Secondly, based on the derived battery health map, the performance of the battery pack will be evaluated for customer specified trip so as to evaluate the “worthiness of replacing” certain modules/cells.