Before we begin, remember that the first person to do this was a fellow by the name of Sorensiim, aka the McGyver of Android, so don't be surprised if you can't do it on the first try or you end up making your device explode into a ball of fire all over your face. WATCH OUT because not only is this a hardware hack, it's dealing with live wires which can give you a bit of a zap. Now that we've got that out of the way, lets talk about what Sorensiim did. It began when he was installing a System Recovery app - he clicked the recovery boot button and found that once booting, he got a message that said "Battery low - cannot program." This is what he did.
First, he grabbed his USB cable and cut off the B plug - that being the side that plugs into the device. Once the shielding was stripped away, he found four wires, one each of White, Red, Green, and Black. Black of course is the ground and Red is +5V DC. These are the ones he needed to make the power flow.
With the Black and Red wires, he stripped back the covering to reveal just the wires (no more than 1-2mm's on each) and pushed them GENTLY into the + and - slots on the battery (the battery found inside the phone, of course, which you've of course had out the whole time.) He applied a tiny bit of tape to keep these wires in place, but made sure to not cover the rest of the connectors.
He then plugged the battery into the phone, making sure that the wires stayed stuck to the battery while the Green and White wires are held back and away.
THE MOST IMPORTANT PART of this process is to make sure that the wires are touching only their correct terminals. If you don't know which is which, DON'T DO THIS STUFF AT ALL, EVER. Why? Because you could make your battery explode and/or fry your phone, and just to be safe, I'll say your face as well.
Red goes to the +
Black goes to the -
He went on to plug the other and of this new USB cable into his computer, allowing the 5V of DC electricity to flow directly into the phone and the battery. He reminds us that this is, of course, very similar to what you'd do if you were jumping your car battery, a thing that I and the rest of my midwest compatriots are very familiar with.
Finally he was able to get his bootloader going (Volume up + power on) and the message "ready to program, connect USB data cable" was seen. He connected his micro USB cable that he of course had a spare of, and connected the other end to his computer. He then let the flashing begin.
The end! Happy cutting and taping! Thank you to Sorenslim for taking the time to do this so that the world might know its glory!