NOVELTY - A first switch such as a relay selectively connects a direct current source to a first equipment having operative components which can be electrically disconnected without a loss of function. A second switch such as a relay selectively connects the direct current source to a second equipment having operative components which can exhibit a loss of function when electrically disconnected.    USE - For delivering electrical power to equipment, e.g. computer, communication equipment, associated with a mobile site such as a vehicle.    ADVANTAGE - Operates to selectively couple battery powered systems to electrical system of mobile site and to a secondary, or back-up battery separate from the primary battery associated with the electrical system of mobile site. Implements logic and filtering algorithms capable of performing various system control functions for providing reverse battery protection, over voltage and under voltage protection, battery drain protection, battery charging detection, reverse current detection and uninterruptible power switching.    DETAILED DESCRIPTION - A battery, separated from the direct current source and electrically coupled with the second equipment, provides direct current for operating the second equipment when the second equipment is disconnected from the direct current source. A processor is electrically coupled with the first and second switches. The processor activates and deactivates the switches to selectively connect the direct current source to the first and second equipment and to disconnect the direct current source from the first and second equipment, respectively. INDEPENDENT CLAIMS are also included for the following:    (A) an uninterruptible DC power supply system;    (B) a process for supplying uninterrupted power to equipment which is to be operated by direct current source; and    (C) a process for supplying uninterrupted power to equipment which is to be operated by first battery and generator for charging battery when generator is in operation.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of the circuit components of the uninterruptible DC power supply system.