Hi!
If the battery is dry, you won’t retain a save file. You can check if the battery is dry or not by saving the game. If you boot it back up and the save is gone, it’s dead. If you wait a day and the save file vanishes, then the battery is going.
If it has a preexisting save file on it, you’re good, but you should change it anyways as you’ll loose the save file when it dies, and you don’t know when it was last changed.
Source: I own many, many, many gen 2 games.
Hope this helps!