Not all Minox cameras (8×11) require a battery to function. You have the Riga/A/B/MX/AX, which are completely mechanical, so they do not need a battery. But some other models do need it, such as Minox C/LX/CLX/TLX/EC/ECX and BL. Lack of battery in any of these last mentioned will not allow for shutter release or meter to work. And this happens because the meter is the one telling the camera what speed to choose; in the absence of a working meter the camera is blind, as it were; shutter does not fire, and the camera is useless. A battery chart which will explain what battery goes in what Minox camera can be found here, if you need one.
Please note that the Minox BL needs a battery only for the meter, otherwise you can use it simply as a Minox A camera, fully mechanical mode.
For any of these Minox cameras to work, one may need a stack of 4xLR43 batteries, a stack of 3xLR43 and 1xLR44, or the 5.6v (e.g. Varta V27PX, or similar) or Exell S27PX (which is actually 4xLR43 stacked in a moulded sleeve). In short, the battery needed (for those cameras that do need it) is the replacement to the old and now extinct 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 currently under several codes: PX27S / RPX27S / 4SR43, most of the showing up on the net under the code S27PX.
One has to pay attention to the voltage, as the original 5.6v for Minox (and the subsequent current models) are specifically designed to maintain that voltage. Mind, using 2xCR 1/3N in your cameras would be bad practice, as the two stacked together are a bit longer than Minox battery compartments are; just a smidgen, but enough to damage your camera. Or use it on your own risk. I have had nasty surprised at the beginnings, when I broke the contacts on a Minox EC, deformed (badly) the contacts in a MInox LX, so word to the wise: do not use these.
Anything higher than 5.6v would (theoretically) making your meter go haywire, or so it is maintained by some. While I can see the reason for this sort of conclusion, I have not seen anything peculiar happening to my Minox cameras when using 6v batteries/battery adapters, in the last 20+ years since I use them. That lucky I am not, not every time, so I guess if something was the matter with the 6v batteries, I would have known by now. The difference in voltage seems to be minute, and it does not influence the meter a great deal.
This brings us to the Minox BL situation, which is a bit peculiar: the battery this camera needs is not of the ilk of those aforementioned. The meter is powered by a 625 battery, (itself replaced by the new PX625A, as the old PX625 is extinct now). However, 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. So, battery=meter, no battery=Minox III/s.
There are reports that the hearing aid batteries are discharging very fast, both models (zinc-air batteries come in several models, with multiple orifices and some models with only 2). The steep discharge curve is due to air action on the battery’s materials, I would assume. Also, there are reports of the Wein Cell battery: some swear by it, some are saying that this battery does lose its charge too quickly. I have used the Wein cell in the past, and I can report that the ones I had in my BL’s were indeed discharging too fast for my taste. Perhaps I got a bad batch.
To end all these troubles, I decided to go MH 44 adapter way. A very small and hollow thing, the same size as the 625 original BL battery. A SR41W cell goes inside this little adapter and fits perfectly. The very small circuitry in the base of the adapter cuts the voltage a tax, so you’ll end up with a 1.35v source in your camera, instead of a plain 1,5v. To my knowledge, this is the only situation where a different battery may cause problems to the meter.
My opinion? If you got lucky and have one of these B: cameras in good shape and with the meter working all right (most of the BL’s I’ve seen lately have their meters reading all over the place or not working at all), I would suggest you should take care of the old boy and use this or any other adapter. Worthy in the long run.