The present invention relates to a battery pack including a battery cell stack including a plurality of battery cells, a temperature adjustment element configured to prevent an increase in temperature of the battery cell stack due to a high external temperature, a heat plate disposed at a lower surface and a side surface of the battery cell stack, a pack case configured to receive the battery cell stack, the temperature adjustment element, and the heat plate therein, and a cooling fan configured to discharge heat in the pack case to the outside, wherein the battery cell stack is configured such that, when external power is supplied to an electrical apparatus connected to the battery pack, the battery cell stack does not supply current to the electrical apparatus, and when no external power is supplied to the electrical apparatus, the battery cell stack supplies current to the electrical apparatus, whereby it is possible to maintain the temperature in the battery pack so as to be lower than the temperature outside the battery pack.