A new model for simulating battery temperature changes from the lower surface to the upper surface is proposed. The cell model is established with experimental calibration. Simultaneously, the cell-to-pack (CTP) model is established through experimental benchmarking. In addition, the thermal properties of CTP and an ordinary battery pack that has an enclosure on the basis were compared under four different working conditions. The results indicate that adding an enclosure to the CTP has little effect on the thermal performance of the battery pack. Adding an enclosure to the CTP hardly improves the temperature uniformity of the battery under cooling conditions; the temperature difference between the upper and lower surfaces of the batteries at both ends of the module drops by approximately 0.5 °C, while the central temperature difference is basically unchanged. Compared with fast charging without cooling, the battery temperature dropped by more than 12 °C under the fast charge condition with cooling. More importantly, the specific energy and packaging efficiency of the battery dropped from 160.27 Wh/kg and 73.1% to 148.72 Wh/kg and 67.8%, respectively, after the CTP was added with an enclosure.