I haven't tried any of my old games in a long time. I remember checking out my Pokemon Silver cart a couple years ago; the clock was shot, but the data was still there. I don't think I tried saving the game again, though. I haven't checked any of my Gen. I carts (2 Red, 1 Blue, 1 Yellow) in probably over 5 years, though.
My copy of Kirby Super Star probably came with a bad battery or something; it constantly erased my files at random from the day I got it back in 1996 or whenever.