The auxiliary electric power supply for a vehicle has a first switch electrically connected to an I/O end; a capacitor bank; a discharge resistance; and a controller. The capacitor bank has series-connected electric double layer capacitors, and balanced resistances. Each of the balanced resistance is parallel-connected to each electric double layer capacitor, and has substantively the same resistance value. The capacitor bank and discharge resistance are connected to the first switch. The controller controls the first switch while monitoring the voltage of the capacitor bank and the operating state of the ignition key operating the ignition switch of the vehicle, so as to connect the capacitor bank to the discharge resistance when the ignition switch is turned off.