Technician Handbook 601 Hybrid Systems for Collision Repair HV Battery Cooling System The HV battery cooling system uses a cooling fan to draw air from the cabin and circulate it through the battery assembly. The exhaust is vented outside the vehicle through an exhaust vent in the trunk. The Battery Smart Unit (Battery ECU) monitors battery temperature and turns the fan on and off as needed to keep the battery cool. 15 Collision Repair & Refinish Training