Abstract: A technique for estimating energy consumption of a portable electronic device is described. During this energy-estimation technique, the portable electronic device determines hardware-state information for communication subsystems that implement different communication protocols, and software-state information for the communication protocols. Then, using models for the communication subsystems, and the hardware-state information and the software-state information, the portable electronic device estimates the energy consumption. Based on the estimated energy consumption, certain percentages of the battery charge may be allotted for different applications or features, battery-life diagnostics may be improved, and useful information may be provided to a user about the battery drain on their portable electronic device.