These cameras have 40-50 years. Better budget for a good CLA and you'll have a new camera for another 50 years. That's what I do with mine. I have 5 FTb; they are excellent; ( not as good as the EF; but fully Manual, metallic and reliable)
Yeah I let my AE-1 sit for a few years with the battery in it. I know..duh. Worked fine and the battery is still going. T'aint cheap but if it lasts years it's OK. I use a Weston meter too. :D
I'd just like to upgrade, really. I picked up an AE-1 because it was cheap. I think I've done my looking and settled on a New F-1. I'm probably going to have to put it on my Christmas list, though, since it's far from cheap enough for me to afford any time soon.
Changing a battery is not a big deal. Everything from your cell phone to your car uses a battery, and all such batteries will eventually be replaced. As for which Canon FD camera to get, the EF is a good camera; inexpensive, and styled after the F1. The FTb is a great camera, and is fully manual. The meter requires a battery (just as the EF does), I simply got an adapter which allows me to use an SR44 battery stepped-down to 1.35 volts. If you have a little extra money to spend, the F1 is the way to go. I prefer the old F1 to the newer versions, they have a certain look to them which I like.
I keep a record of when I change my camera batteries, and the PX 28 Lithium battery I have in my Canon A1 has been in it for nearly eleven years and is showing no sign of packing up, I'm going to replace it today because without a doubt I've certainly had my moneys worth. :)