This paper describes the development of and tests performed on a Battery Management System (BMS) that was developed for lithium ion based cell chemistries. The BMS follows a universal architecture developed to support multiple chemistries. It estimates and reports the State of Charge (SOC), State of Health (SOH), State of Life (SOL), and Power Availability of the battery pack. The BMS also reports current, cell voltages, and temperatures. Additionally, the BMS performs active and passive cell balancing and fault protection via solid state circuit breakers. The BMS package conforms to military requirements, including an operational temperature range between -55°C and +70°C, and provides a Controller Area Network (CAN) interface. Algorithm accuracy performance was quantified in the laboratory. The BMS consistently demonstrated accuracies within 5% SOC in a software upgradeable, low cost package. Currently we are performing field tests on a U.S. Army ground combat vehicle.