I recently checked all mine (within the last few weeks), and the only one that has died is Gold, which died a few years back. The rest are working (including my 1998 Blue Version), and I actually just played through Yellow again (and am in the process of beating Crystal). I won't bother changing the battery though. When they finally die, I'll just use an emulator. I have all of the important details saved on my computer (teams, pokemon caught, etc), but I never really go back and play the ones that I beat and never restarted.
Edit: @SecondWar: I can't comment on the DS games, but I've had my Ruby version since it first came out, and every time I start it up, it tells me I won't get any time based events anymore. It is the original save file too.
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