Remember, you should only do this, for the most part, for a temporary time. Otherwise, your phone could break slowly over time (due to unstable surges of power from time to time), and no one knows yet if there is protection against it.
*This method may work on other models of the Samsung Galaxy S III
For those looking for a way to get their phone up and running without a charger may now do so, but before you start please pay attention to the important information first.
An official Samsung battery for the Samsung Galaxy S III gives off power at 4.2 V (no matter how much energy storage, when fully charged)(https://en.wikipedia.org/wiki/Battery_(electricity))
Official recommendation for a highest energy input to the phone via energy source (usually via battery output/USB charger output) is 5.25 V
*Thanks to paccer for this ^ information
USB 2.0 ports will only give off 100mA unless the device requests for more... up to 500mA (make sure you know what type of port it is... others may give off 500mA by default and go higher!)(https://en.wikipedia.org/wiki/USB#Power)
You're going to need the following:
1. A usb cord of any kind that you're willing to cut up
*For those who are experienced, if you have wires already then make sure to have the vcc and gnd)
2. Some sort of device with a USB 2.0 port (not sure about 3.0, and 1.0 might not be enough) that gives off energy from a device such as a computer, gamingconsole, etc.
3. Electrical Tape (other tapes may work if they are nonelectric and have enough adhesive to stick)
2. A wire stripper (the scissors may work, just be gentle)
First off we need to label some parts and describe what they are for (I'm pretty sure I have this right)
Now it's time to know where the wires will go (overview so don't do anything yet)...
Obviously we want the VCC pin connected with the VCC wire and the GND pin connected to the GND wire.
Then essentially the phone (when pressing the power button) should turn on...
*Sometimes the phone won't turn on/turns off after being on, this may be because of loose wires so just try to refold the wires onto the pins.
1. Make sure the back of the phone is open and ready
2. Use the scissors to gently cut off the outer part of the USB cord (make sure not to cut into the wires inside!)
3. Strip the ends of the VCC and GND wires by about a centimeter so we can use them on the pins
4. Connect the wires to the pins
A. Loop the exposed VCC wire through the VCC pin and fold it back to tape to phone (make sure it's not
touching any other metal)
B. Repeat step 4 A for the GND wire and GND pin.
5. Test your phone by turning it on... if it works then welcome
Proof of it working (sorry for the bad quality, only had an old 3DS to record with):
Instead of haveing it plugged in a computer I had a different power source called the PocketJuice (http://tzumi.com/manuals/Solo2000mAh.pdf) which supplies a bit more power than a USB 2.0 port
(I made sure before I used my power bank that it had an okay voltage, so don't go testing your portable power banks unless you listened to the warning at the very top of the post)
(didn't remember that I had internet on so that's why the first game I tested didn't load and the PocketJuice is visible after 1:39)
Samsung officially supplies support that can be given from visiting their website for a live chat, sending an email to them through their official form , or by calling their phone number at 1 (800) 726-7864