Energy management of an electronic device using multiple electric power sources. The electric power sources may include a parasitic electric power source, a rechargeable electric power source, an intermittent electric power source, and a continuous electric power source. The electronic device further may include a power supply for receiving the electric power from the source(s) and supplying electric power to the various components of the electronic device that require power. The electronic device may include a source selector for controlling which power source supplies electric power to the power supply. Energy management of the electronic device may be configured to use a permanently exhaustible power source such as a battery only when other power sources are unavailable.