For extended backpacking trips, old MP3 players or Gameboys that you no longer have love for can be a great source of entertainment. Unfortunately, AA batteries are way too small for extended use. After the first couple hours, they die, and then your Gameboy is just extra weight to pack out. But wait! D-cells and AA's are both 1.5V battery cells! In fact, the only difference is that D-cells have more juice. Sadly, that means they're bigger and won't fit your tiny Gameboy. However, all you need is some speaker wire, cardboard, plumber's tape and a hot glue gun to more than quadruple your game time.

Step 1: Make a Box

It's not hard to make a box. Simply figure out what size box you need to contain two D-cells (as demonstrated in the pictures) and apply duct tape liberally. Your box will eventually be a battery pack.

Step 2: Add Contacts

You need something to carry the electricity to the wires on the outside of the box. Use plumber's tape to create contacts and use the hot glue gun to attach them to the OUTSIDE ONLY. Don't attach them on the inside, it just doesn't work.

Step 3: Attach the Wires

Separate the speaker wire into two separate wires. Strip both of them in two places as shown and duct tape them to the contacts so both exposed parts are touching the contacts. Cover them in duct tape. Don't hold back. You want it to last .

Step 4: Make the Replica Battery

Cut out two pieces of cardboard that are the length of a AA or AAA battery (depending on what you want to use it for) and attach them with duct tape. Look at the pictures for a more precise explanation. Put the wires through so they come out on the opposite side from the one you put them in through. Fill up the fake battery with hot glue, but not all at once or it won't work. Use your freezer to make it solidify faster if you are impatient like me. Once it's full, bend the exposed ends of both wires over the ends of the batteries. This is demonstrated, once again, by the pictures. Use a little bit of hot glue to attach them.

Step 5: How Can I Customize This for MY Specific Needs?

These are all ways you can customize the super battery if it's not quite working for you. Skip this part if you're creative or if it works for you as is. Treat the separate paragraphs as entirely different steps. Read them out of order if need be.

I was lying earlier, you can't use this for a Gameboy. This is because Gameboys require two batteries. There are two ways you can work around this.
1. Make a double-size replica battery and use two battery packs. It's a bit more work, but if you put in that extra work you will be glad you did.
2. Just use a regular AA for the second battery. I'm pretty sure it'll draw most of the power from the D-cells. If not, revert to plan A (#1).

Remember, if something doesn't quite work, it's okay to stray from the instructions a little. In case you're like a lot of people who don't get the concept of ingenuity, I'll restate that in big letters.
YOU DON"T HAVE TO FOLLOW THE RULES EXACTLY! THAT'S RIGHT! YOU CAN CHANGE IT AND IT WILL STILL WORK!
When things are made of duct tape and cardboard, there's not a very strict recipe. With things that are manufactured, the instant you remove a screw they break. Not so much with cardboard.

As I said earlier, if your device takes AAA's, just modify the replica battery size to be a AAA. Not too hard. You can even do it with watch batteries, although you should bear in mind that they put out 3V, so you'd need to link your D-cells in series (with this they're linked in parallel). If you don't know what series and parallel are, look them up. It's a good thing for everyone to know.

Since this is intended for camping and backpacking, you might want to make battery pack impervious to the elements. I recommend getting a plastic organizer box from Walmart (a small one is about $4) and cutting out six pieces of that thick plastic to make a box out of (use hot glue to attach the edges). You can even put a hinge on the lid and use a magnet to hold it shut.

Step 6: Add a Lid (If You Want)

A lid can be handy if you want to add a bit of aesthetic appeal, or if you don't want stuff to get in or, if you're like me, just feel like a lid is the right thing to do (what would it be without a lid?). Just take another piece of cardboard, duct tape it to the box on the inside and outside so it won't peel off, and you've got a basic lid. If you want it to lock, try using a magnetic clasp like I did. I took a shard of a hard drive magnet and glued it to the front of the box on the opposite side from the duct tape hinge, then I folded a piece of plumber's tape over the front of the lid. It's as simple as that.

Step 7: Proof of Concept

As you can see in the photos below, this actually works. If you do it right, it will do what I say it will. Curiously enough, I found that despite the fact that the batteries are linked in parallel, the battery pack will only work with two batteries that aren't empty.

Step 8: Viola!

And now, a few afternotes. As I wrote the plastic box idea in step five, I realized that it would make a good Instructable in and of itself. Feel free to steal it for yourself if you like, as long as you credit me somewhere. Also, if you want to use this as a part of something you build and post on this site, feel free to do so without even crediting me. However, I would really appreciate it if you did. As an aspiring musician, I think creative license copyright laws suck, so all of my stuff is pretty lax.

Now you're done!
Have fun with your Gameboy in the wilderness!