Abstract: A fail safe power supply system specially adapted for supplying power to devices such as lights. A battery is provided to supply power to the devices, and during normal operation, charge on the battery is maintained within selected levels by a charging control system that is connected to a source of commercial power. During a commercial power outage, the battery continues to supply normal power to the devices for a prolonged period of time, usually until commercial power is restored, thus obviating the necessity for a separate backup power source.