Cartridge Batteries
Some of your carts have probably been around for quite a few years now, and the ones with Battery Backup for your saved games and high scores may be forgetting that info :-(
Anyway, it's an easy fix, pop in a replacement battery, easy if you can get the correct battery with solder tabs on.
I STILL haven't done this to any of my carts yet, but if you've just picked up a cart to play through - maybe replace the battery beforehand, give your game a further 10 or more years battery life!
This place sells the batteries AND has links to guides to fit them.
