This is a really simple task, and can only really cost you up to $8.00 (If you have the parts). So, just read along! There isn't much you have to know, only how to solder (It's melting metal, how hard can it be?) and use scissors.
Step 1: Materials and Tools
Alright, for this, you'll only need a few basic things.
--Solder Iron, Solder Wire (Buy it here for $8.00)
--NDS Charger, USB Cable (Lite or Launch, Type-A Male)
--NDS (Lite or Launch) of course ;D
Also, recommended, you only use the chargers provided by Nintendo. These will last MUCH longer than 3rd party chargers.
Step 2: Setting Up the NDS Wires
This is really simple.
--Cut The NDS charger as stated.
--When you have the cable cut, you'll see that one wire is thicker than the other. Strip off some of the "shielding" of the wire to expose it.
--All you have to do know is twist the wires on top of themselves. The NDS is now done!
Step 3: Setting Up the USB Wires
This, as well, is very easy.
--Cut the USB cable as stated.
--When you have the cable cut, you'll see that there are four wires instead of 2. There is red, black, green, and white. Cut away the green and white wires, you don't need them.
--All you have to do know is twist the wires on top of themselves. The USB cable is now done!
Step 4: Soldering
This is one of the easiest things to do. If you bought that kit I mentioned, use the guide to help you if it's your first time soldering.
--Take some soldering wire, put it to the red wire, solder that, adn do it with the other red wire with the same strip of soldering wire. Now surrond the soldering wire and red wires in electrical tape. Do the same for the black wires.
--Wrap some more electrical tape around both set of wires to keep the wires from getting caught on something and snapping.
Step 5: Credits
The Instructible was mad by me.
The original tutorial was made astrangeone on GameFAQs.
Nintendo DS was made by Nintendo.
And a bunch of other credits I don't want to list :P