THERMAL STATE OF CHARGE ESTIMATION OF PHASE CHANGE MATERIAL (PCM) IN A BATTERY PACK WITH A PCM THERMAL MANAGEMENT SYSTEM

A method and apparatus for determining and/or monitoring a thermal state of charge or melt fraction of phase change material in a battery system. The battery system includes a plurality of electrochemical cell elements, a supply of a phase change material in thermal contact with the plurality of electrochemical cell elements, and a battery management system that monitors a thermal storage capacity of the phase change material and automatically controls a power of the plurality of electrochemical cell elements as a function of the thermal storage capacity of the phase change material. The battery management system automatically adjusts a power output of the plurality of electrochemical cell elements as a function of the thermal storage capacity of the phase change material to provide a heat output within a predetermined safe temperature limit.