Abstract: A portable power system for a hand tool employs a high-voltage transmission of power from a battery pack over a cord to a DC to DC converter, which steps the transmission voltage down to rated tool voltage. The system uses a switching transistor to transmit power according to a duty cycle which varies automatically according to tool current draw and voltage. The DC to DC converter employs synchronous rectification with an inductor-capacitor network to transform a duty cycle square wave into DC power. The startup voltage sense feature permits powering up the converter circuitry only when needed. The converter will shut down if no current has been drawn by the tool for a predetermined period of time or if the converter unit is in danger of overheating, as determined by a stored algorithm. The portable power system has safeguards to prevent fouling or shorting in wet environments, is adaptable to left or right handed users, and is physically configurable into a variety of carrying modes.