The present disclosure is directed to a heat flux assembly for an energy storage device. The energy storage device includes a housing with a plurality of side walls that define an internal volume and a plurality of cells configured within the internal volume. The heat flux assembly includes a plurality of heat flux components configured for arrangement with the side walls of the housing of the energy storage device and one or more temperature sensors configured with each of the plurality of heat flux components. Thus, the temperature sensors are configured to monitor one or more temperatures at various locations in the plurality of heat flux components. The heat flux assembly also includes a controller configured to adjust a power level of each of the heat flux components as a function of the monitored temperature so as to reduce a temperature gradient or difference across the plurality of cells during operation of the energy storage device.