Most Game Boy games (and by that I mean the pre-Advance time) are saved into the cardridge and powered by a battery so that this memory will not vanish.
In a future, far far away, the battery empties, which will lead to a loss of the save state as there is no power source to hold the save state in the memory.
A solution is to replace this little battery and have a saveable game again. So I'm now playing Dragon Warrior Monsters and achieved pretty much everything in the game. I know I will play that game again (as I replay it often since release).
My fear is that I will lay back the cardridge until digging it out again. By that time the battery may already be empty (never replaced it since I bought the game).
What are my options if I want to replace the battery precautionary and keep my save game?
(This may include tinkering tips, extra hardware or a simple "won't erase your save game anyway".)
I ask this question specifically for the "pre-Advance" GameBoy cardridges: