Aux battery pack for all your USB powered gadgets.
A group of friends and I go hiking every year and I like to plot our trips using the GPS in my phone and the Google Tracks application. Trouble is 6+ hours of full time GPS use tends be a major drain to the battery. In previous years I had purchased commercial versions similar to this, they only lasted about a year, and were not as high capacity as I was able to build here.
I found that I was able to keep my phone running for about two and a half days with this battery pack.
Battery - http://www.sparkfun.com/products/8484
Charger/Booster - http://www.sparkfun.com/products/10300
Print all three parts.
Mark and drill the holes to hold the charger/booster circuit.
Drill out the holes for the two sides. --I found that the sides printed better raft-less when the screw holes didn't go all the way through.
I had intended to use the on board micro USB socket for charging and connect a the female end of a USB extension cable for discharging. Trouble is over time the on board micro USB socket broke off.... :( so I ended up soldering in both the male and female ends of the USB cable.
Assemble, Charge... Discharge...
At some point I need to add a switch between the battery and the charge/boost circuit. If I understand correctly, the charge/boost circuit has a constant draw that will eventually drain the battery.