Old Nintendo hardware and cartridges may last forever, but the batteries inside some games (used to save progress) do not. With an expected lifespan of only ten years (though they can last much longer), we're obviously well past the point where you can expect all save games to work for a console like the SNES.
So if you're still dabbling with older consoles, you'll need a fix. And this handy guide at Motherboard is just that. With handy pictures and practical tips, it shows you how to crack open a SNES game and replace the watch battery that powers the cart's ability to save games.
While the cart in question is Link to the Past, it should work for just about any SNES game that needs a tune-up.
Note that swapping out the battery won't salvage your old save games; once that battery is gone, they're gone. But with a dead battery you can't save at all, so this fix lets you get back in the game. Well, back in a new game, which you can then save.
How to Replace an SNES Cartridge's Save Game Battery [Motherboard]