Apple, like any device maker, struggles with the problem of maintaining reasonable battery life in gadgets that are growing increasingly smaller.

The company was today granted a patent for a portable fuel cell power source that could feasibly be used to power the iPhone or other devices for up to weeks at a time.

The design consists of a “fuel stack” that converts the fuel into power, and another receptacle for the fuel itself. A controller manages the operation of the fuel cell system. An interface transfers the power to a portable computing device like a phone. A communication link between the device being powered and the fuel cell communicates how much power is needed.

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Apple defines a “portable computing device” as a laptop computer, mobile phone, personal digital assistant (PDA), portable media player, digital camera, or other type of compact electronic device.

The patent is credited to inventors Bradley Spare, Vijay Iyer, Jean Lee, Michael Hillman and David Simon. The patent was originally filed way back in 2010.

Apple filed another, similar patent in 2011 for a fuel cell technology that both contributes power to and takes power from the battery in a mobile computing device. But that patent may still be under review.

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