A battery based power supply assembly is disclosed. The system comprises a discharge initiating device and a plurality of battery modules electrically connected with one another. Each of the battery modules comprises a plurality of battery cells, a discharge load connected in series with the battery cells, a switch coupled between the battery cells and the discharge load, a temperature sensor, and a controller adapted for placing the switch in its electrically connected state upon being driven by the discharge initiating device. The invention further provides a safe method of draining the energy from the power supply assembly disclosed herein.