quote Jolt135

It's been over 6 years since Pokemon Gold was released, and that's a ripe timeframe for seeing complaints that players' game cartridges are no longer saving data.

This observance is almost universally the result of a dead save battery. Game Boy games put all their alterable data (such as player status) in RAM, but one thing to know about RAM is that it's volatile. A constant supply of power must be provided, or else all of the memory gets reset. Of course, since players can't be expected to leave their game plugged into the system and turned on all the time, any game with a save file uses a small battery to supply power, keeping the RAM from switching itself off. In Gold/Silver/Crystal, the battery is also used to power the in-game clock.

It doesn't take much electricity to power the clock and memory to a satisfactory extent, but you are dealing with a small battery and a long period of time. After 5-7 years, the battery is expected to die. When the time comes for you (or if it already has), rather than getting a whole extra copy of the game (which is likely to be used, and its battery may not have much time left either, forcing you to repeat the process all over), it's possible to replace the save battery and start fresh. In this topic, I hope to explain how, and enable the reader to perform the operation on their own.

First off, you need to open up the game. It's held together by a screw, but Nintendo used an obscure screw type so that the consumer isn't likely to be able to open it up. You won't find it in your average store either, but there are lots of online merchants out there, and some of them are bound to have the right driver. If you search on eBay for "nintendo 3.8mm", you should get relevant results.

Once you're in, you need to replace the battery. Most Game Boy games use a CR1616 coin cell, but Pokemon R/B/G/S/C (not Yellow) use the larger CR2025. (The 2025 in the name means that the battery is 20 millimeters in diameter and 2.5 millimeters thick; the same convention holds for the rest of the CR line such as 1616 or 2450). Unlike the 3.8mm inverse-star driver, you can find CR2025 batteries at a store, at the display stand where they keep button and coin cell batteries for watches and other small devices. My local Target sells them for $3.19 each, which is fine if you don't want to go through the hassle of buying those online as well. If you do choose to buy batteries online, you can get them (usually in packs of 5) for $1.00 or less per battery. Beware of 2 things: 1) Avoid batteries that say they ship from Hong Kong; this is often the sign of a dubious seller who will have their item "confiscated" at customs and leave you with no recourse (shipping takes an inordinately long time from there in any case), and 2) many of the listings you'll find are for obscure brands that skimp on the reactants, resulting in batteries that don't last as long--stick to well-known brands such as Energizer, Maxell, or Panasonic.

Once you have the driver and the battery, open up the case. The battery has a metal contact stuck on it (and there's also another contact underneath it). You need to pry the battery free of the contacts. Use a small, sharp knife and try to squeeze it under the contact, then twist it under you break the solder points. Then lift up the battery and do the same for the bottom contact. If the contacts bend a bit, that's fine; you just don't want them flying completely off the circuit board, rendering it useless for running a connection from the battery.

Now you'll replace the battery with your fresh one. If you have access to soldering equipment, you can use that to re-fashion a sturdy connection between the battery and the contacts. If not, a good deal of electrical tape will suffice. Wrap it around the battery and the contacts, keeping them stuck together while also using the tape to shield the battery from forming an electrical current with extraneous parts of the circuit board, which could potentially ruin your game to the point that battery replacement won't fix it.

Now just close the game up, fasten the screw in, plug it in, turn it on, and see if you can properly save again. If your battery isn't yet dead, but don't want to risk losing your file when it inevitably does, you might want to invest in a device called the "Mega Memory Card" for Game Boy. It'll let you back up your save, and though replacing the battery will cause power to stop flowing to RAM for long enough for the game cartridge to lose track of it, the MMC stores saves in non-volatile memory. After changing battery, you can restore your save file to the point it used to be.