AAs in the booster are designed to be more of a stop-gap measure than for continuous use. They drain very quickly.
They only stopped producing the EOS 3 last year, I believe. I would not worry about the batteries too much.
I would be more worried about film in 10 to 20 years than I would be about batteries. As soon as the motion picture industry goes digital, film will be on its last legs almost literally overnight (as if it is not already). They may keep making black and white, but not unless colleges continue to be staffed by those who push film as a learning medium. Judging my the recent influx of young, dumb, digitally-raised professors at my school, I would not count on that. Expect a bad economy to hasten this demise, as it already has, with people always seeking the most economical way to work. Remember that professional digital cameras have not even been around for a decade, and look what they have done to the industry. The end started with Clive Howes of Getty Images making the decision to transmit the first digitally-captured image over the wires. That was just sniper fire, however. Then, it's kind of like a nuclear bomb hit Film Town as soon as the D1 came out, and we film users are all the survivors of the attacks. We've made it till now, but the fallout will get us eventually...
