Never have owned a Canon camera in my life. I've managed to go 56 years without ever shooting with one.
Then today, the Magic Postal Truck drops off a package at my door. I have been gifted a Canon FTb with a 50/1.8 lens.
It needs a good bath, and the leather case it came in is totally gone. But at least the shutter & aperture seem to work reasonably well. So after I give 'er a good scrubbing, it'll be time to run some film through 'er and see what's she's got.
Nice find Sparky. I'll be looking for an A1 soon. I haven't had a Canon since I sold the AE-1 about 12 years ago. So I guess all my Nikons will see the A1 as an infestation
You can also use a rubber "O" ring with a 5/8 inch outside diameter and a 7/16 inch inside diameter from any hardware store to space the battery chamber.
Costco sells 675 hearing aid batteries in packs of 30 for pennies each.
The hearing aid batteries have good discharge curves, and mimic fairly well the behavior of the 625 mercury cells that the FTb was designed for - they just don't last as long.
Some cameras need a metal adapter like the ones I got from Jon Goodman, because contact with the metal edge of the adapters matters. Others will work fine with the rubber O rings.