My wife was playing a Harry Potter game on the Gameboy Color, and a few weeks ago she turned it on and her save was no longer there (and a language screen popped up). So I bought a brand new battery and replaced the old one. Everything went well. She started playing again, but after about two weeks her save disappeared again (and the language screen came up).

Note, this is the Europeon version, which is why there's a language screen where you select what language you want the game to be in.

I would like to know if there are "non-battery" reasons for losing saves on a GBC game. The second battery worked fine for a while, so I don't think it was a bad battery. Could there be a glitch? Thanks for your help.