Abstract: A reserve power system for a commercial AC load provides DC power to the load when the primary power fails by providing direct current voltage power from a DC power source which enables the load to continue to operate in a normal fashion. A power system supplying commercial AC derived power to a load provides backup power by coupling DC power to the load when the primary AC power fails. AC power is supplied to a primary winding of a power transformer which also has a secondary winding side. A cable is connected, at a first end, to the secondary winding side and at a second end to a load powered by a commercial AC voltage. A battery DC voltage source and a battery charger are connected to the secondary winding side of the power transformer. The battery charger maintains the integrity of the reserve power. A voltage monitoring circuit connected to the power transformer detects a primary power failure and activates switching circuitry for connecting the DC voltage source directly to the load.