How to Make a Portable and Rechargeable USB Charger

Clear all the mints and paper out of the Altoids tin (mints can be put in a plastic bag so they can still be eaten.)

Find a female USB port. These ports can frequently be found on USB extension cords.

If using a USB extension cord, cut the wire as far away from the part in which you plug in the wire you wish to extend. Strip the wires Find the black (-) and red (+) wires. Make sure these are separate from the green and white data wires.

If your wires are very short, (less than 9 inches) you may want to extend them by soldering wire to them. Be careful not to add too much as it may not fit in the Altoids tin. About 9 inches (22.9 cm) branching off of the female USB should suffice.

Put your 4 rechargeable AAA batteries into your battery holder. For now, they do not need to be charged. (Hint: rechargeable AAA batteries can cheaply be bought on eBay or a similar auction site. These batteries are rated by the amount of power they can store not the power that they output. The units used are milli-Amp hours (mAh), which can be explained as the current (in milli-Amps) needed to fully discharge the battery in an hour. A 1000 mAh battery will last twice as long on one charge as a 500 mAh battery. AAA battery holders can cheaply be bought from Radio Shack, make sure it will fit in the Altoids tin--this usually means to buy the thinner square looking one--see picture in Things You'll Need.)

Connect the wires from the battery holder to your USB wires. Remember red to red and black to black. Soldering is usually the way to go. Other methods are twisting the wires together, but this is unreliable. Remember to cover the exposed connected wire in insulated material (like PVC or electrical tape) to avoid letting the positive and negative wires touch.

Make a square shaped hole slightly larger than a USB port in one side of the Altoids tin. If using a Dremel, beware of sparks that can ignite flammable materials. Make sure it is one of the shorter sides--not the sides above or below the text--to the left or right only.

Put your battery holder connected to your female USB in the Altoids tin. Make the ON/OFF switch (if your battery holder has one) to the battery holder is up so that when you open the tin you see it the female USB port not stick out of the USB port, but have it line up so it doesn't stick out.

Hot glue the female USB port in place. You can also put double sided tape or hot glue on the battery holder so it doesn't move.

You may close the tin. Your charger is now complete. If your batteries are uncharged, follow the last step to charge.

Make a male to male USB cable if you do not already have one. Cut the ends off 2 USB cables, leaving as much wire possible after the USB connector. Strip the wire exposing the colored wires. You may cut the white and green wires. Strip the red and black wires. Connect the wires together (red to red and black to black) by soldering or wire twisting (unreliable.) Cover the individual wire connections together with electrical tape, having 2 separate pieces (cover the black to black separately and red to red separately.) Then after the reds and the blacks are separately covered in tape, you can cover these connections with electrical tape so you are left with a single wire.

To charge--using your Male to Male USB cable, plug one end into your computer (or USB AC Adapter) and one into the USB port of your charger. Your charging. After a few hours, charging is complete.