I love the Mintyboost power supply/charger Instructables, but wanted to look for something a little readily available that doesn't see much use anymore and that was a little easier to customize. Going through a few stores of odds and ends, I came across an old cassette tape collection, and there it was! I tossed in a $1.69 Radio Shack 7805 5 volt regulator (they have virtually every type of protection built in, including thermal overload, spiking, reverse polarity, etc.), and came up with this! It's easy, fast, and a great little charger that you can use with just about any DC power source to charge your cellphone, or, with a little extra effort, your USB! A big thanks to JDurban for his advice on this project!
Step 1: The Regulator
Step 2: The Simple Version
I went ahead and used an old leftover female USB port (leftover from a motherboard add-on) instead of wiring directly into my cellphone wire, as I had a USB charger adapter readily available. I also used alligator clips which would allow me to attach any available DC power power supply, including batteries, instead of wiring directly to a DC wall wart.
Here you can see that I'm actually charging my cellphone from a 9 volt battery! 4-6 AAs also work, and even a cordless drill battery...