BlueStar Advanced Technology Corporation (BATC), with the sponsorship of the USAF and Canada's Department of National Defence, is developing large (20 to 50-Ah) Li ion cells for use in aircraft and spacecraft. The effort initially explored the graphite/LiCoO2 chemistry packaged in both cylindrical and prismatic configurations and then focused on cylindrical designs while continuing to explore variations on the basic chemistry which would optimize specific energy and capacity retention. Several generations of the 20-Ah cells have been fabricated and tested. 20-Ah cylindrical cells have been delivered to the USAF and are under test at JPL and Sandia National Laboratories. More recently the cylindrical design has been extended upwards to 45-50 Ah and downwards to 5-7 Ah. These cells have been characterized with respect to capacity, rate capability, low temperature performance and cycle life.