the invention relates to plug - compatible modular thermal management packages of small elevated temperature devices that act as easily replaceable miniaturized sources of power , heat , or chemical reaction products . the modules may be solid oxide fuel cells , combustion heat generators , or miniature chemical reactors . the devices operate at elevated temperature in sealed , insulated thermal envelopes . the technology permits such devices to operate in a thermally efficient manner that minimizes heat loss to the environment . the thermal management packages are easily replaceable when spent .