I'm in charge of designing a battery bank (using 18650 batteries) that will produce large amounts of heat for a short period of time. The battery bank will be in a near vacuum (~800 Pa), so convective heat transfer will not be effective. Since the operation time is only ~80 seconds, my thought is to store the heat in paraffin wax. The battery bank will be placed into an aluminum box (coated with electrical tape spray to insulate it) and be raised from the bottom of the box with a polycarbonate sheet between the batteries and the aluminum. Paraffin wax will be poured into the box in direct contact with the batteries and allowed to solidify at room temperature. Initial calculations show that it will easily be able to store the heat generated. Now, I have concerns about putting the batteries in direct contact with the paraffin wax. Will the wax prevent the batteries from venting and possibly lead to an explosion? Or are there other possible issues with direct contact?