A method and apparatus that allows for controlling operating time of a portable computer system and a peripheral device. A portable computing system that includes a rechargeable power supply and that includes a connection mechanism for coupling to a peripheral device is used to control operating time of the portable computer system and the peripheral device. In one embodiment, a user can choose between maximizing the operating time of the portable computer, maximizing the operating time of the peripheral device, or maximizing the life of the entire system (maximizing the operating time of the portable computer system and the peripheral device). When operating time of the portable computer system is to be maximized, power is sent from the peripheral device to the portable computer system to extend the operating time of the portable computer system. Similarly, when operating time of the peripheral device is to be maximized, power is sent from the rechargeable power supply of the portable computer system to the peripheral device to extend the operating time of the peripheral device. When operating time of the entire system is to be maximized, power is moved such that the operating time for the portable computer system is equal to the operating time of the peripheral device.