If the battery dies or you lose it and you can no longer use it, then you can no longer log in to the game. To remove it from the SE account requires you logging in with it to begin with, so after you've lost it/the battery has died, you can't remove it either.

Maybe I should have worded it better to avoid snarky comments, so here goes. If the battery dies and we can no longer use the key, how then do we log in to our accounts?