This paper describes the development of a Battery Management System (BMS) State of Charge/Health (SOC/SOH) algorithm that was developed and proven for three different lithium ion based cell chemistries (nanophosphate, lithium manganese oxide, lithium iron phosphate). In addition, a universal BMS architecture based on this algorithm was developed that can support other chemistries, capacities, and formats. Algorithm performance was compared to actual data in the laboratory environment and also to data from a lithium iron phosphate hybrid electric vehicle pack that was integrated with an XM1124 hybrid electric HMMWV operating in a vehicle environment under realistic conditions. The system demonstrated accuracy within 5% in a software upgradeable, low cost package.