That looks like the correct battery at 7dayshop. The voltage should be 1.35 or 1.4 volts. I cut a very thin slice of plastic 1/2 inch cpvc plumbing pipe to center the battery. I also have some O-rings of the right dimensions to center the battery. The O-ring numbering systems vary, even among suppliers here in the US. The one you see mentioned on the internet is a #13, but I forget the dimensions, which are in fractional inches. If you can't find a reference for the size, get back to me and I'll see what I can find. You should be able to get the zinc-air 675 at almost any chemists. Once you have the battery and camera in hand, you could fit a proper O-ring at a local hardware store.
I've never used autofocus at all, or even read about it in the magazines. It's quite possible, perhaps likely, that the two people I mentioned weren't using it properly, so I'll reserve any final judgement on autofocus until I've used it properly myself. The last time I looked at a new SLR to see how it worked was 1983. The one I use is a 1977 or 1978 design, so I'm really outdated in that regard. That one has an auto-exposure mode, which I used once in 1981 shooting on fisherman's wharf in San Franciso.
There are no hyperfocal markings on the Canonet, but mine has two scales, meters and feet. I think what may be confusing you is the aperture scale. It has f-stops from 1.7 to f:16, then a red A for shutter speed priority with auto aperture, the on the other side of the red A are numbers 28, 20, and 14, which I recall as being the guide numbers for use with the dedicated flash. I don't have that item. The lever for changing the ASA has window, cloud, and sun symbols, but there is a real numerical ASA scale as well.
If you want a DOF scale for any lens and use Windows, visit dofmaster.com. You can download a free program there to print out a DOF dial scale to your own specifications. There's another program there for printing out a hyperfocal chart for multiple lenses. Nice stuff.
Having a Copal leaf shutter, the Canonet is far quieter than any focal plane shutter.
One thing that I haven't mentioned that I like about the Bessas is the trigger winder. You can find info on it at cameraquest.com, and possibly also Robert White. I can get between 2 and 2.5 frames/second out of it, and I like the grip and bulk it adds to fit my large hands. It's an all mechanical trigger advance that's reasonably quiet, no batteries. I understand that either the Hexar or Contax (perhaps both, I haven't used either) has a reasonably quiet motor advance as well.