The original lithium battery pack in hybrid Ford Escape consists of 250 nickel metal hydride cells with a nominal voltage of 1. 25 V and capacity of 6 Ah each. All cells are connected in series to achieve the nominal voltage of 330V with a capacity of 1. 98kWh. The total weight of the cells is 45 kg and the total pack weight is 65 kg. If the capacity of our lithium ion pack was to be equivalent in weight and volume to the existing Ford Escape pack then it would have a capacity of 5. 0 kWh. For an engine-dominant, charge-sustaining hybrid system such as Ford Escape Hybrid, the battery capacity is not critical as the typical charge-discharge pulse energy is quite small, in the order of 50 Wh. The key criterion is the power capability of the lithium battery pack. In the case of the Ford Escape, the powertrain power demand can be met by a small battery with a capacity of 2. 0kWh. A maximum discharge current in the system reaches 160A and a maximum charge current reaches 80A. However, to reduce thermal loads and improve life of the battery, a with a capacity of 3. 0kWh was chosen. The weight of the cells in the pack was 24 kg and the total pack weight is 39 kg. In order to reduce the development time, the original lithium battery packcomponents were used where possible. The nickel-metal hydride cell assembly was removed and replaced with the lithium ion cells.