What causes a SNES game to lose its save game?
Let's sum up what we got. Possible reasons:
- Battery fault.
- SNES fault (for some reason erases saves randomly).
- Cartridge fault (memory chip corruption).
So that's that you can do:
- Be sure you replaced battery nice and correctly.
- Try other games, and see if their saves are not lost.
- Try cartridge on some other SNES console and see if it fails there.
Try the capacitor next to the battery on the cartridge circuit board - I just replaced the battery in a SNES game and noticed there were dry joints on both capacitor pins.