A battery pack is provided. The battery pack includes first and second temperature sensors that are disposed in first and second interior spaces, respectively. The first temperature sensor generates a first signal indicative of a first temperature level of the battery cell. The second temperature sensor generates a second signal indicative of a second temperature level of the DC-DC voltage converter. The battery pack further includes a microprocessor that determines a first desired operational speed value of the electric fan based on the first temperature level, and a second desired operational speed value of the electric fan based on the second temperature level. The microprocessor selects the first desired operational speed value if the first desired operational speed value is greater than the second desired operational speed value.