Carefully dismantle the plug. Remember to make a note of which wire is connected to which pin. I forgot to do this so i had to use this webpage: http://pinouts.ru/Slots/USB_pinout.shtml
Step 2: Soldering
Solder on small leads, this makes it easier to solder on the chunkier leads. Cut the leads to an appropriate size and solder on the leads from the charger. The small wire connecting pin 2 and 3 is there so the phone can recognize that a charger is plug in (2 and 3 is usually for data).
Step 3: Finishing with Sugru
When you're done soldering, finish of with Sugru to make the strong, durable and to avoid short circuit.