Abstract: A thermal jacket adapted to accommodate and cool a storage battery placed in the engine compartment of an automobile and exposed to heat at elevated temperatures emanating from the engine. The walls of the rectangular jacket are formed of rigid, foam-plastic material which thermally isolate the battery from the engine. Embedded in a wall of the jacket is a heat exchanger in which there is circulated a refrigerant fluid derived from the air conditioner installed in the vehicle. The heat exchanger acts to cool the battery to maintain the temperature of the electrolyte therein at a level at which the battery operates at optimal efficiency.