I think you're a little confused, of course a battery can't store digital information. These cartridge console games saved into a RAM that was powered by a battery, so it wasn't erased when the cartridge was out. The battery lasted very long because the RAM consumed very little power, but to my knowledge after too many years when the battery died, your saves would be erased. And I don't think they used rechargeable batteries. And there wasn't any provision for the save feature to be repaired, as cartridges weren't meant to be opened; but even so you'd have already lost your old saves. And pre-emptively replacing the battery before it died would also erase your games, unless you provided a bypass power supply for the while when there's no battery.
http://en.wikipedia.org/wiki/Saved_game
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On later cartridge-based console games, such as Kirby's Adventure and The Legend of Zelda, saved games were stored in battery-backed RAM on the game cartridge itself.
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http://en.wikipedia.org/wiki/File:Po...ilverBoard.jpg