I have recently acquired a Canonet 25, which lacks a battery. I have been unable to find an original instruction manual, and I have no idea as to what the original battery should be. The inner of the cap indicates 1.3V (and this obviously means a mercury cell). The best I could figure out is RM450 or PX450: they both have a diameter of 11.6mm and a height of 14.5mm. What would be the best solution for a replacement.
I strongly assume that the QL25 used the PX1 cell as this one was the one many Canonet cameras of that aera used. The PX1 has the same diameter as the PX625 and the PX640 but it is higher. The 625 and a spring should be the right choice to operate the camera.