Heating element and circuit managing equivalent series resistance of energy storage cell

An apparatus and method of keeping an energy storage cell at or above a target temperature, includes receiving at a processing circuit, an analog voltage that is proportional to a temperature of the energy storage cell, converting, at the processing circuit, the analog voltage to a pulse-width-modulated signal having a duty cycle that is proportional to the analog voltage, and driving a switch, with the pulse-width-modulated signal, between conductive and non-conductive states to modulate a voltage passing across (or a current flowing through) a heating element in series with the switch, the heating element being in thermal communication with the energy storage cell, wherein the duty cycle of the pulse-width-modulated signal is adjusted to maintain the temperature of the energy storage cell at or above the target temperature.