Replacing a video game cartridge battery without losing saved data

Back in the 8-bit and 16-bit video game days, a small number of game carts contained a battery in them. They used a small lithium battery to allow games to be saved on the cartridge. Before the 8-bit days I don't think they had saved games, and after the 16-bit days they used flash memory. So this is really a small number of 8-bit and 16-bit games that have batteries. But these batteries won't last forever, in fact most of them are probably dead by now. Amazingly enough I have a cartridge at home that still has saved game data 20 years later!

Replacing the battery isn't too difficult as long as you have some soldering skills, but doing so will erase any data saved on the cartridge. I own Phantasy Star 2 on the Sega Genesis (Mega Drive) that has some pretty incredible saved games that I want to preserve. So this is my attempt to replace the battery without losing saved games.

1. Opening the cartridge
This step may seem straightforward, but it may be more complex. The Sega Master System used standard philiips screws, but the Sega Genesis uses a security bit. So you may need to buy a security bit to open the cart, or find another creative way to open it. Once open you need to identify the type of battery. All Sega carts I've seen use a CR2032 lithium battery. Here are pictures of the front and back of Phantasy Star 2.




2. Buy replacement batteries
Once you know the type of battery you need to order replacement batteries. Yes, you need to order 2 batteries for this to work. I highly recommend you order "tabbed" batteries. Soldering directly onto batteries is difficult and can be dangerous. These replacement batteries should be fairly cheap. I got mine from newark for $2.57 each.


3. Add a battery in parallel
For this technique to work you need to solder a second battery onto the cartridge in parallel with the existing battery. In theory this battery will continue to provide power while replace the battery soldered into the cartridge itself. When soldering in this second battery be sure and get the polarity right.


4. Replace the battery
With the temporary battery in place, you can now desolder the old battery and solder in the new one. Removing the battery is very easy with a solder sucker, or you should be able to get it our using just solder wick. Once the original battery is out you can solder in the new one. You may need to bend the pins so they align with the holes in the circuit board. Also, as before make sure you get the polarity correct. Here's a picture of the new battery soldered to the board after I removed the temporary battery.


You can now reassemble the cartridge and try the game out. When I did here's what I got:


FAILURE! Crap, I just lost all my saved games.

So what happened? Well I can only think of one reason why this failed. Soldering requires very high temperatures, so the circuit traces around the battery were briefly subjected to temperatures in excess of several hundred degrees. A general rule of electricity is as temperature increases so does resistance. So my guess is the resistance increased causing a drop in voltage and current sufficient to cause a lose of stored data.

Is there a way to get around this and still make it happen? I can think of two ideas. First, if you used a voltage source higher than a single lithium battery (3.6V) the increased voltage might be enough to overcome the increased resistances from heat. Of course, this becomes tricky because too much voltage could "fry" the chips on the circuit board. The only other suggestion I can think of is to buy a retrode. This device allows you to read and write saved game info directly from the cartridge. So you could save the data to your computer, replace the battery, then restore the data.

Well even though my attempt was a failure, I'm glad I did it. It was a fun project, and these new batteries should last another 20 years.