Operating temperature has a significant impact on the performance, safety, and cycle lifetime of the lithium-ion batteries. The operating temperature of a battery is the result of the ambient temperature augmented by the heat generated by the battery. This paper presents the empirical investigation of the effect of ambient temperature on the performance of a Lithium-Nickel-Manganese-Cobalt-Oxide based cell with 3.6V nominal voltage and 20Ah capacity. The experiments are carried out in an environment chamber using five controlled temperatures at −20°C, −10°C, 0°C, 20°C, and 50°C, as the ambient temperatures. In each controlled temperature test, a constant current (10A, 20A, and 40A) continuously discharge the cell to a cut-off 2.5V. The cell discharging voltages and usable capacities are the battery performance indicators. The experimental tests show that discharging voltage at 50% DOD and the total discharging time to reach 2.5V (usable capacity) increase as the ambient temperature increases. The modeling and simulation of a battery cell temperature model is built in the Simulink platform. The correlations show that simulated and experimental discharging curves match well in the 0–80% DOD range and the discrepancy is under 7%. The developed simulation model could provide thermal management guidelines for lithium-ion polymer battery applications in 12 voltage SLI, start-stop, and 48 voltage mild hybrid electric vehicles.