It is an open secret that Pentax 6X7 and 67 don’t run without power. While their mirror and cloth curtains are mechanically driven, they are in fact electrically controlled by transistors and a magnet. A TTL prism finder drains a battery if you forget to switch it off. The most common equivalents to PX28 are well-known alkaline 4LR44 and silver-oxide 4SR44 batteries. While you can find these batteries in some specialised stores, they are not universally available in case you’ll need them urgently.
And it happened with me once… I forgot to take batteries for both my cameras – Pentax 6X7 and 67 – on a trip and was unable to instantly find a 4LR44/4SR44 battery or its equivalent in the town I was staying. Fortunately, I managed to find four LR44 button cells instead keeping in mind to fix them together with a tape and use the whole set as a replacement.
It was a big success to find them so easily and quickly in a nearby store. These batteries are more common in local stores than 4LR44/4SR44. But they are also a bit longer then a set of four LR44/SR44 button cells. So, I needed a spacer of about 4-5mm long to be added to the set.
Considering “what to use as a spacer”, I found an iron screw-nut of similar diameter and about 7mm long lying on a street, which I used as a spacer. The set is 3mm longer than a standard 4LR44/4SR44 battery, but it is still possible to be used as a replacement for PX28.
Well, it was a good experience and the set sufficed for the entire month of shooting and I kept using it upon my return for some time. Honestly, it is better to use original 4SR44 or 4LR44 batteries. I will be happy if my tip helps you in a difficult situation. Wish your batteries never let you down and keep shooting!