Soldering Iron. Best if its mounted in a stand, with a tip cleaning sponge, or some other form of tip cleaner.
Solder spool (60/40 rosin core)
Flux (probably not required here, but handy to have.)
Solder wick or Solder sucker.
3.8mm game bit + driver.
CR2032 battery holder. (Harwin Inc. S8421-45R, available at Digikey or mouser.)
SNES game cartridge which needs its battery replaced. :)
Step 1: Taking the Game Cart Apart.
If the battery is not yet dead, and there is a save still present, if you have a retrode, now is the time to make a backup of this save. :)
Step 2: Removing the Original Battery
The method I use to do so, is to heat up the smaller negative tab, and when it is hot enough, pull on the battery to release it. Repeat the process with the positive tab.
If you are lucky, the holes will be cleared of solder, and you can proceed to the next step. If not, that is where the wick or your solder sucker tool will come in handy. Get the holes cleared out.
Step 3: Modding the Battery Holder.
Since this holder is originally a surface mount part, we just have to make a few tweaks to make it a through-hole part, suitable for this application.
First off, we want to straighten both the positive and negative terminals.
Once we are done that, the next step is to clip a little bit off of the negative terminal using your diagonal cutters. (The positive does not need to be clipped, as it is 2.8mm wide. The negative unfortunately is 1.8mm wide, just 0.3mm too wide to insert as is.)
Step 4: Mounting the Battery Holder
Step 5: Inserting New Battery and Putting the Game Cart Together.
Then, put the game cart back together.
If you have previously made a backup of your save with a retrode, back in step 1, now is the time to restore it. :)