I have a couple of NES games that use a battery to save your game. The only problem is that after 20+ years the batteries are starting to die. I have decided to try and change the battery in a game. I ordered replacement parts from The Nintendo Repair Shop. On the way is the bit I need to open the games and the correct battery with the solder tabs. I have also purchased a couple copies of Ultima Exodus just in case I screw up. When all the parts come in I plan on documenting the whole process.
Wish me luck.