Some of the Minox cameras are purely mechanical, some are not. Therefore, the models that are not entirely mechanical need batteries in order to operate at all. There are also some cameras that work without battery, if you do not need the meter.
The Minox 8×11 cameras that do not need battery to operate are: Minox Riga, Minox A/IIIs (and of course the model II and III), Minox B, Minox MX, Minox AX. All other Minox 8×11 cameras need a battery to work. These are: Minox C, Minox BL, Minox EC, Minox LX, Minox CLX/TLX. And evidently, their respective accessories, mainly the flash units to go with these cameras.
Old type mercury EPX27/PX27/V27PX, 5.6v, now extinct.
The exceptions here is the Minox BL camera; it has a meter powered by a 625 battery, (itself replaced by another type, as the old PX625 is extinct now), but if the meter is not powered for some reason, the camera is a regular A/IIIs, as all the functions are mechanical. This is made possible by the fact that the meter is uncoupled, and is there only to provide separate reading for setting the shutter speeds yourself.
The battery needed (for those cameras that do need it) is the replacement to the old mercury PX27 of 5.6v (also known as EPX27, V27PX, 4NR43, KX27, HS3C, PX27, PX27A, RPX27A, 4LR43, 4AG13), now replaced by a similar alkaline one, similar voltage, known under several codes: PX27S / RPX27S / 4SR43, most of the showing up on the net under the code S27PX.
One of the best replacements on the market today.
If you live in Europe somewhere close to the British Isles, you may buy it here: Small Battery Company. They are serious people, bought from there a couple of times and been satisfied.
And of course, you have the alternative to use a battery adapter. Minox made one which is very good, using 4 x 386 cells, stacked on top of the other. Because the total of the voltage adds up to 6v, the adapter has a metal bottom which takes down the voltage to a regular 5.6v.
There are several other types of battery adapters on the market, some made by 3D technique even. But when you consider the adapter to be a simple plastic tube, filled with a stack of 4 batteries, it becomes clear that one can make such a device oneself. Easy: take 4x 386 cell batteries, wrap them with a thin piece of selotape, and stuck them in your camera. Or dismantle an old battery (non mercury) and use the plastic sleeve inside. They will work. You understand this solution is a temporary one, until you procure some proper battery for your Minox.
I myself use a stack of 1 x LR44 and 3 x LR43, which work very well in my cameras. Obviously, this is only an emergency solution, for I usually have proper batteries (PX27G) in Minox cameras I own. I buy them from here: The Acumulator Shop. It is located in Romania, but this type of battery PX27G should be found in most of the European countries (you may get it here on Amazon). It is very good, I have had no issues with it whatsoever. Granted, it’s 6v not 5.6, but I have not noticed any problems with the meters or anything like that.
I have made a chart with the battery replacements for Minox cameras and their accessories. I have put it here for your perusal, and if you have any need of clarification, do not hesitate to contact me.