Whenever I’m away from home for an extended period of time, I would charge my phone and mp3 player from my laptop. This way, I get about 3 or 4 full charges out of the laptop battery and I could leave the phone and mp3 player chargers at home. The device is based around a DC/DC boost circuit, a microcontroller (I used a PIC12F683) , and a handful of 18650 lithium-ion cells. Laptop batteries usually contain 8 of these cells (although I notice my netbook only uses 3, which explains the dismal battery life). I harvested the batteries for this device from an old Dell laptop battery, but you can buy 18650 cells cheaply on ebay, (you can see one in the top right of the picture below),.