The oldest are my Tennokoe Bank hueys. I got 'em 10 or 15 years ago when they were already at least a decade old.
Ah, yes. That's a good one. I have one as well and it was still a working a year or two ago when I used it last, and it may be older than my Neo Geo memory card.
I just used mine (Tennokoe Bank) last week, so, damn, I guess that counts.
I think most of my NES games still work (I haven't tested them all in the last year, though...only a few).
I know that my SNES/SFC and Gameboy crap has been very mixed (a lot of dead batteries)....
...of course, I always wondered if it was due to the fact that I bought a lot of used games that might have been stored under horrible conditions.
You see, games that I purchased new have held up well.
I was curious if anyone had figured out the "math" behind the energy drain on a battery in a cart and, guess what?
http://atariage.com/forums/topic/193374-battery-life-of-old-game-cartridges/I have no idea if this is reliable info, but I found it incredible that a battery could, theoretically, have a lifespan of 70 years.
Corrosion and other physical failures could occur, I reckon, even if the storage conditions are appropriate.
Still... 70 years for an NES cart?
Damn.