An efficient and safe operation of lithium ion battery packs for electric and hybrid electric vehicles requires maintaining the operating temperature of battery packs within the optimum range. This paper models and assesses the performance of an ammonia boiling based battery thermal management system to maintain the operating temperature of possible future ammonia based hybrid electric vehicles within the optimum operating range. A battery pack design of an ammonia boiling based thermal management systems is proposed, modeled and analyzed. In the proposed design, the batteries are partially submerged in a liquid ammonia pool, and the ammonia pool boils through absorbing part of the heat generated by the battery at the surface submerged in the liquid ammonia. This cools the battery and produces ammonia vapor. The ammonia vapor cools the unsubmerged part of the battery through forced convection heat transfer. The generated ammonia vapor passes to the vehicle electrical generator, where it is used to produce electrical energy for driving the vehicle or charging the batteries. The performance of the each proposed design is assessed for various design parameters, for a 600 s discharging and charging cycle at a high rate of 4C. The results show that the ammonia boiling based battery thermal management system performs better than liquid and air cooling systems. The electrical energy use of the proposed system is nearly negligible compared to that for liquid and forced air cooling systems.