Hello,
So I recently picked up Pokemon Gold on eBay for super cheap because the saving feature was broken.  For those of you who don't know, Pokemon Gold and games like it store their saved data in a special kind of RAM called SRAM.  Since RAM requires a battery to keep the data intact, these cartridges have a small battery inside.  Usually, when your game stops being able to save, it's because this battery died.  Unfortunately, the kind of battery they use can be difficult to find.  I decided to use an alternate battery in its place - a AA.
Obviously a AA battery can't fit inside of a GameBoy cartridge, so I had to do a lot of hacky stuff to make this work.  The first thing I did was scrounge up some equipment.  I don't have any solder, or a soldering iron, or even any proper wires.  The materials for this build are as follows:
-Cheap plastic pen
-Lighter
-Old noise-cancelling headphones
-Speaker wires
-Tape
-Scissors
-AA Battery

These are all the materials I used for this.  The first thing I did was get the cartridge open.  I took the ink and metal tip out of my pen, and melted down the tip.  While it was still hot, I pressed the tip of the pen onto the screw that held the casing on (it requires a special screwdriver that is difficult to find).  After the melted plastic pen dried, I had a DIY GameBoy cartridge screwdriver.  I removed the screw and opened up the case to reveal the game inside.
Attached to the game was a battery powering the SRAM.  I pried it out of its casing, leaving the contacts in place.  Then I looked for some wiring and found speaker wire.  This I stripped.  I wound some of it around each contact and left it aside.  Then, using the lighter to soften the plastic, and scissors to manipulate it, I put some holes in the side of the casing so the wires could get out.  I put the game back in the case and led the wires out.
I went to look for something to hold the battery with.  After a lot of searching, I stumbled upon some old noise cancelling headphones that had a mount for a single AA battery.  I abused the headphones until just the mount remained, and put a fresh battery inside.  I trapped the leads coming out of the cartridge between the battery's contacts and the walls of the mount.  I then stuck the cartridge back into my GameBoy Advance and turned it on.
I went through the prompts and chatted up Professor Oak a bit, then finally was dropped into the overworld and saved the game.  I turned off the GameBoy, crossed my fingers, and started it up again.  Hooray!  The game offered me the option to continue, and I was able to save again.

Pics of the build below:

Hmm, I've been having problems with Silver...it "saves" but it's corrupted quite a bit.  Won't load.
Looking at the instructable linked from IRC, it should work with a watch battery
(admittedly I have yet to see a CR2025, but it's lot like I've looked around either )

I wonder if it'd be usable with the calculator's 5th battery?

I wonder if you could desolder the SRAM and replace it with a Zero-Power SRAM. 

Please don't double post, but instead edit your previous post to contain the new information.

Thanks!

I could have used the lighter a lot less, but it made the plastic easier to work with.  Especially the headphones, they were an inch thick.  Without the lighter, it would have taken forever, but 10 seconds on the flame and scissors did the job.

Wow nice Sir, you should move this to general hardware/electronic discussion.

Congrats on fixing The Game.

I remember some SNES games where the batteries died and my Super Metroid/Ys III and Illusion of Gaia save data would be gone if I stopped playing for more than 24 hours or so.