This is also battery powered so it is portable and you can use it when there is no outlet available. I'm eventually going to put a relay in mine so it automatically turns off the battery pack, when I plug in the adapter. But for now, I'm just going to show you how to build a functional soldering iron that just works. This is not to difficult of a project so i'm sure you can get it done.
If you are going to build this you will already need to have a soldering iron so you can solder the battery holder, switches, etc. If you do not have one you could probably twist the wires together and put electrical tape around them, but I don't know how well that will work.
Disclaimer: Soldering irons can be dangerous if not used properly, do not let the hot tip touch yourself anything flammable. You can easily burn yourself or start a fire if used improperly. I am not responsible for any damage or injuries that occur.
Now that we got that out of the way, let's head on over to the next step to show you what part's you'll need.