US Patent 7863856 Bi-directional battery charging for coupled electronic devices

A system for bi-directional battery charging, including a first electronic device, including a first rechargeable battery, for providing power to the first electronic device, and a first battery charger, and a second electronic device, including a second rechargeable battery, for providing power to the second electronic device, a second battery charger, a voltage boost that receives an input voltage from the first rechargeable battery and is selectively enabled to either up-convert the input voltage as input to the second battery charger, or else to passively pass the input voltage to the second battery charger; and a controller for programmatically controlling the first and the second battery chargers and the voltage boost, wherein the second electronic device attaches to the first electronic device to operate in combination therewith, and wherein the controller is programmed to decide, based on the voltages of the first and the second rechargeable batteries: (i) whether to supply power to the second electronic device from the first or second rechargeable battery, (ii) whether to charge the second rechargeable battery from the first rechargeable battery, and (iii) whether to enable or disable the voltage boost. A method is also described and claimed.