A fuel cell system for a portable computing device, wherein the fuel cell system comprises: a fuel cell stack which converts fuel to electrical power; a fuel source for the fuel cell stack; a controller which controls operation of the fuel cell system; and an interface to the portable computing device, wherein the interface comprises, a power link for providing power to the portable computing device, and a bidirectional communication link for providing bidirectional communication between the portable computing device and the controller for the fuel cell system, wherein the bidirectional communication link communicates fuel cell state information from the fuel cell system to the portable computing device via the bidirectional communication link, the fuel cell state information comprising one or more of: a state-of-charge of an internal rechargeable battery within the fuel cell system; a pressure at an inlet of the fuel cell stack; a pressure at an outlet of the fuel cell stack; cell voltages for individual cells in the fuel cell stack; and certification information for the fuel cell system; wherein the bidirectional communication link communicates fuel cell control information from the portable computing device to the fuel cell system, and wherein the fuel cell state information and the fuel cell control information are used in one or more feedback-control loops to actively control one or more operating parameters of the fuel cell system. a fuel cell stack which converts fuel to electrical power; a fuel source for the fuel cell stack; a controller which controls operation of the fuel cell system; and an interface to the portable computing device, wherein the interface comprises, a power link for providing power to the portable computing device, and a bidirectional communication link for providing bidirectional communication between the portable computing device and the controller for the fuel cell system, wherein the bidirectional communication link communicates fuel cell state information from the fuel cell system to the portable computing device via the bidirectional communication link, the fuel cell state information comprising one or more of: a state-of-charge of an internal rechargeable battery within the fuel cell system; a pressure at an inlet of the fuel cell stack; a pressure at an outlet of the fuel cell stack; cell voltages for individual cells in the fuel cell stack; and certification information for the fuel cell system; wherein the bidirectional communication link communicates fuel cell control information from the portable computing device to the fuel cell system, and wherein the fuel cell state information and the fuel cell control information are used in one or more feedback-control loops to actively control one or more operating parameters of the fuel cell system. a power link for providing power to the portable computing device, and a bidirectional communication link for providing bidirectional communication between the portable computing device and the controller for the fuel cell system, wherein the bidirectional communication link communicates fuel cell state information from the fuel cell system to the portable computing device via the bidirectional communication link, the fuel cell state information comprising one or more of: a state-of-charge of an internal rechargeable battery within the fuel cell system; a pressure at an inlet of the fuel cell stack; a pressure at an outlet of the fuel cell stack; cell voltages for individual cells in the fuel cell stack; and certification information for the fuel cell system; a state-of-charge of an internal rechargeable battery within the fuel cell system; a pressure at an inlet of the fuel cell stack; a pressure at an outlet of the fuel cell stack; cell voltages for individual cells in the fuel cell stack; and certification information for the fuel cell system; wherein the bidirectional communication link communicates fuel cell control information from the portable computing device to the fuel cell system, and wherein the fuel cell state information and the fuel cell control information are used in one or more feedback-control loops to actively control one or more operating parameters of the fuel cell system.