It is well recognized that weight savings within an airframe can result in significant lifetime cost savings and increased flight range. The transition of aluminum alloys to lighter, composite materials is an increasingly prevalent strategy to reduce weight on aircraft. This paper describes the application of a lightweight carbon fiber composite technology to aviation, engine start lithium batteries. The transition of lithium battery chassis technology from metal to composite introduces technical challenges not found with traditional battery chassis. Modern lithium batteries contain more than energy cells; common internal components include switch mode battery chargers, health and safety monitoring electronics, and even environmental control circuitry such as heaters. Consequently, electromagnetic interference disruption potential created by the electronics must be addressed. Moreover, insulation material, heaters and/or cooling technologies may be present which traditionally worked in companion with metal casings. This is not the case for composite chassis: the challenge of dissipating internal heat increases with a carbon composite chassis compared to that of aluminum alloy because of the differing thermal material properties. Additionally, the carbon composite material must be carefully designed so as to not introduce a flammability risk. This paper describes the design, development and evaluation of a composite chassis prototype for a large engine start lithium battery that meets the traditional aluminum chassis EMI capabilities, complies with industry standards for vibration and flammability resistance, and supplies sufficient electronics grounding capabilities for aerospace lithium batteries.