Thermal management of battery systems

This invention relates generally to battery power supply and, more particularly, to thermal management in such battery power supply systems. The word "battery" here is meant to include various forms of electrochemical power generation which have in common that chemical energy, in the form of one or more chemical reactants stored in a confined space, react with each other or with an external reactant in an electrochemical reaction, so as to produce electric power when desired. The invention is to a method of operating a power supply system comprising the steps of discharging at least one cell element of a battery module to produce a quantity of power and a quantity of heat; absorbing at least a portion of the heat in a phase change material in thermal contact with the discharging cell element; following discharge, releasing at least a portion of the heat from the phase change material to heat the at least one cell element; and discharging the at least one cell element at elevated temperature.