Battery Case Power System

A battery case is operable with an electronic device such as a cellular telephone. The battery case has a battery that can be used to supply power to the electronic device. The battery case is configured to receive power from a power supply that is coupled to a mains power supply using a wired path or to receive power from a wireless charging mat or other wireless power transmitting device. Circuitry in the battery case may include direct-current-to-direct-current power converter circuitry, current sensor circuitry, switching circuitry, and other circuitry for controlling currents and voltages in the battery case and communicating with other electronic devices.