Battery pack thermostat

The utility model discloses a battery pack constant temperature device which comprises a lower protective shell, supporting plates are fixed to the two ends of the upper portion of the lower protective shell, a cold and hot circulation system and a battery module are arranged between the two supporting plates respectively, and the battery module is located above the cold and hot circulation system. A winding mechanism is arranged between the cold and hot circulation system and the lower protection plate; the two pieces of heat preservation cotton can be independently wound under the condition that the influence on the heat preservation effect of the heat preservation cotton is small, the airtight film and the air valve assembly are arranged outside the heat preservation cotton, air in the heat preservation cotton can be pumped out through the vacuum pump, the winding diameter of the heat preservation cotton is small, and therefore the bottom space of a vehicle is saved. The heat preservation cotton of the bat