Battery PX14, 2.6v, 2.7v, 2.8V, 3v.....

Alcayatas · Jul 11, 2025

Hello,

long time ago I was bought a super8 camera Carena 756, and photometer battery ask for a PX14 battery of 2.6V. I couldn't find this battery, and I used two button 1.5v battery, so as a result I have a 3V battery. But unfortunatelly the film was overexposed due to this, so this slightly differences was afectation on the film exposure.
Some time later, I bought another super8 camera, and inside there was and old battery PX14, but to 2.7V. So was a different voltage, for the same battery number? Even today we can find some bateries at 3V. I know this kind of batteries are used also in other photo, and cinema cameras, or photometers.
Some shops also sell a equivalent , or two A675 1.4V battery, so you get 2.8V. also named as a PX14 replace battery. Other sell a 3V battery for equivalent.

So I always have some questions about it.

-What they do this differents types of voltage batteries and give it the same name PX14? 2.6v, 2.7v,
-What they decided do a very different voltage battery, as usuals, like 1.5V, 3V,... It is not easy manufacture the cameras to standards voltages?

Thanks

Nitroplait · Jul 11, 2025

The old batteries were mercury based and abandoned/prohibited due to environmental reasons. These batteries were widely used because they were long lasting and had a good depletion profile. Cameras were made to expect the voltage of these batteries, typically 1.3-1.4V and multiples: 2.7V-2.8V, 5.4V-5.6V

The current closest available substitute is zinc-air (hearing aid batteries) which will provide a voltage and depletion profile similar to the mercury - but zinc-air will last much shorter.
They will often need to be adapted as they are not meant to be used in cameras, but in hearing aid devices.
Wein makes some overpriced substitute batteries if you don't want to adapt common Zinc-Air yourself.
There are dumb zinc-air adapters available on eBay and elsewhere.

Modern cameras are typically made to use alkaline (1.5V), silver oxide (1.55V) or lithium - if you use these batteries in old cameras calibrated for mercury batteries, you will often need a voltage converter to avoid a too optimistic meter reading.
Sometimes you can just compensate by adjusting the ASA/DIN setting - but the resulting readings may not be linear throughout the scale.
Voltage converter adapters will often cost more than the dump adapters.

Examples of battery converters: https://www.kantocamera.com/english/adapter/adapter_en.html

beemermark · Jul 11, 2025

More likely reason was the camera meter failing.

Dan Fromm · Jul 11, 2025

I've used Gossen's PX14 adapter https://gossen-photo.de/en/produkt/battery-adapter-set/ with good results in my Canon 814AZ. See https://www.smallbattery.company.org.uk/sbc_px14_adapter.htm, who sell the same adapter, for dimensions.

https://polarbearcamera.com/products/px14-adapter seems to do much the same but doesn't seem to reduce/regulate voltage, so must be used with the appropriate hearing aid batteries.

336v · Aug 13, 2025

I've recently gotten a couple of Luna Pro light meters and learned about the issue powering them. Being an EE I've [of course...] decided to design and make a proper battery adapter supplying 2.7V from a lithium battery replacing stack of two original PX625 mercury cells. Not a diode voltage drop thing (that works better than nothing, tested that, but that's not really a very stable voltage source).

So I've tested 4 different parts to see which would be the best overall: Diodes' AP7350-27CF4-7, Toshiba's TCR3UG27ALF and TI's TPS78227DDCR and TPS7A0228DBVR - all micro-power voltage regulators. Standby current consumption is quite negligible, around 400nA, which guarantees standard 3.3V Li cell to work for several years. The TPS7A0228 has even lower standby current - just 25nA which is remarkable (my measurement revealed 35nA for the sample chip on hand), but that reg is only produced with 2.8V output. That is just 3.7% more than nominal 2.7V, well within tolerance of two former mercury cells. So powering something like Luna Pro would not be an issue - I've tested these light meters powering them from a variable power supply and within +/-0.2V the pointer remains within red BATT CHECK swatch, e.g 2.5...2.9V range is technically OK. At least for this gadget.

In my tests a +/- 0.2V voltage change makes the exposure reading deviate by +/- 1/3 EV. Powering from 2.800V source resulted just 1/6 EV higher readout than powering from 2.700V.
Rough estimation on the back of a napkin reveals that with even with 500nA standby a standard CR1/3N which is 175mAh capacity, it will take 175*10^6 nAh/500nA=350,000 hours to discharge one cell constantly connected to the regulator. That is 14,583 days or 40 years. A cell will die from the self-discharge far before that. Not to mention life time of its owner so I don't thing this is a concern.

Anyway, I've mounted the chips on a flexible PCBs wrapping around CR1/3N lithium cell - it works just fine, though mechanically this design could be improved - it's difficult to assemble by hand. There was a minimum required order to produce these PCBs, so I ended up with way too many - about 60 or 70 extra assembled adapters that could be put to better use than collect dust in my parts bin. Would that be something people would be interested to acquire for their Luna Pro's or any other photo equipment that meant to use a stack of two mercury cells? I'm not planning to make money on these, that's a hobby project, but just recovering cost of manufacturing these prototypes would be nice.

If there's at lest mild interest from people to try these, I'll move the thread to classified section, but asking here because not sure if it even worth bothering.

If you have an opinion on the subject, please share. Thanks in advance!

ic-racer · Aug 13, 2025

Wow, very elegant solution. I would want one if I had that meter.

How about a 'wrap' like that with a 1.35v voltage regulator for a single cell. That might have more use to the average photrio reader.

336v · Aug 13, 2025

Do you mean a replacement for a single PX625 mercury cell (size wise) for any cameras or photo equipment that was designed to use just one of those cells?

It is not difficult to resize (shorten) the side link with regulator ship to make the stack one cell tall (not two stacked cells tall), but how do I know if such a wrapped
cell will fit into your hardware?

I suppose it will fit as song as overall dimensions of such a wrapped PCB design do not exceed former PX625 mercury cell.

But I don't own any vintage photo equipment, however I know many of those cameras cameras use built-in light metering. I just have no idea how
much more common was to power any of those cameras with a single 1.35V cell rather than with two cells in series. Can you give me an idea?

F4U · Aug 13, 2025

usually a batter over-voltage causes underexposure.

koraks · Aug 14, 2025

336v said:
If there's at lest mild interest from people to try these, I'll move the thread to classified section, but asking here because not sure if it even worth bothering.

From a moderator's perspective: thanks for setting it up this way. I've highlighted your post to the team so we can step in and help out if/as necessary.

bernard_L · Aug 14, 2025

@336v : Thank you a lot for the information.
I had a quick look at the datasheet for the Toshiba part, having in mind adaptation from silver oxide (1.55V) to 1.35V supply. At first I was disappointed by the dropout spec, of order 500mV for the lower voltages. BUT, looking at the curves, as long as one is happy with "only" 50mA, this component works down to almost zero dropout. For my own purpose I would rather incorporate the regulator into the camera body, since the SR44 has the same dimensions as a PX675, leaving no room for the electronics inside the battery chamber. For a PX625/mercury replacement, it is another story.

336v · Aug 14, 2025

bernard_L said:
@336v : Thank you a lot for the information.
I had a quick look at the datasheet for the Toshiba part, having in mind adaptation from silver oxide (1.55V) to 1.35V supply. At first I was disappointed by the dropout spec, of order 500mV for the lower voltages. BUT, looking at the curves, as long as one is happy with "only" 50mA, this component works down to almost zero dropout. For my own purpose I would rather incorporate the regulator into the camera body, since the SR44 has the same dimensions as a PX675, leaving no room for the electronics inside the battery chamber. For a PX625/mercury replacement, it is another story.

Two comments on this:
- I never thought of adapting a single alkaline or silver oxide cell (1.55V at best) to a 1.35V power source, as you've noticed this leaves virtually no room for the dropout. Such a setup might work initially, but as soon as the source voltage drops to 1.4V, this will stop working, 50mV is way too small dropout allowance for even 10mA load. If I were to do it, I'd take lithium cell and regulate 3V nom. to 1.35V. This allows very deep discharge of a Li cell (2.5V is considered totally dead) and it will still provide 1.35V output with plenty (>1V) of headroom for the reg. dropout.

- I just put both - 357 cell (identical to SR44 size wise) and modern PX625 replacement made after merc. cell dimensions) side by side (attached) - they are very different. Yes, a PX675 is listed as the same size as SR44, meaning it's smaller than PX625 seen on attached photo. So, if your camera uses a PX625, the SR44 sized cell has plenty of room around it for three required regulator components - the IC itself and two capacitors. If your camera uses a PX675, the SR44 with electronics may or may not fit - I guess depends on the size of the battery compartment - how much extra room is designed around it.

In my unrelated project, I've used 2mm thick Li cells (SR1220). If I were to make a 1.35V replacement for mercury cell, I'd use two of SR1220 stacked back to back to double capacity and this still would leave plenty of room (1.3mm) for electronics AND PCB above it, not on the side of it. But first I'd look for the largest single Li cell that is still smaller than the SR44 to start with - something that would fit into a compartment meant for either PX675 or PX625 cells. Stacking two Li cells (electrically in parallel) would work, but isn't the slickest idea.

ic-racer · Aug 14, 2025

336v said:
Do you mean a replacement for a single PX625 mercury cell (size wise) for any cameras or photo equipment that was designed to use just one of those cells?

It is not difficult to resize (shorten) the side link with regulator ship to make the stack one cell tall (not two stacked cells tall), but how do I know if such a wrapped
cell will fit into your hardware?

I suppose it will fit as song as overall dimensions of such a wrapped PCB design do not exceed former PX625 mercury cell.

But I don't own any vintage photo equipment, however I know many of those cameras cameras use built-in light metering. I just have no idea how
much more common was to power any of those cameras with a single 1.35V cell rather than with two cells in series. Can you give me an idea?

I was thinking of something that, yes, wrapped around a single LR44 cell. Looks like this PX625 adapter could easily be slotted to accommodate the voltage regulator.

336v · Aug 14, 2025

336v said:
Two comments on this:
- I never thought of adapting a single alkaline or silver oxide cell (1.55V at best) to a 1.35V power source, as you've noticed this leaves virtually no room for the dropout. Such a setup might work initially, but as soon as the source voltage drops to 1.4V, this will stop working, 50mV is way too small dropout allowance for even 10mA load. If I were to do it, I'd take lithium cell and regulate 3V nom. to 1.35V. This allows very deep discharge of a Li cell (2.5V is considered totally dead) and it will still provide 1.35V output with plenty (>1V) of headroom for the reg. dropout.

- I just put both - 357 cell (identical to SR44 size wise) and modern PX625 replacement made after merc. cell dimensions, I think it's a zink-air replacement since has two holes in it. Side by side comparison is attached - they are quite different. Yes, a PX675 is listed as the same size as SR44, meaning it's smaller than PX625 seen on attached photo. I've seen a ring adapter around 675 making it 625-like. I believe the difference in diameters is 2mm, which is the thickness of the ring. So, if your camera uses a PX625, the SR44 sized cell has plenty of room around it for three required regulator components - the IC itself and two capacitors. If your camera uses a PX675, the SR44 with electronics may or may not fit - I guess depends on the size of the battery compartment - how much extra room is designed around it.

In my unrelated project, I've used 2mm thick Li cells (SR1220). If I were to make a 1.35V replacement for mercury cell, I'd use two of SR1220 stacked back to back to double capacity and this still would leave plenty of room (1.3mm) for electronics AND PCB above it, not on the side of it. But first I'd look for the largest single Li cell that is still smaller than the SR44 to start with - something that would fit into a compartment meant for either PX675 or PX625 cells. Stacking two Li cells (electrically in parallel) would work, but isn't the slickest idea.

336v · Aug 14, 2025

ic-racer said:
I was thinking of something that, yes, wrapped around a single LR44 cell. Looks like this PX625 adapter could easily be slotted to accommodate the voltage regulator.

This will not be feasible since the top of the adapter surface will have to be output at 1.35V while inner walls of the same metal chunk are at 1.5V input voltage. E.g. the top of the cell you're using will have to be isolated from the top of the complete adapter solution, so a solid metal adapter won't cut it, even if you slot it to fit required electronic components . Pictured adapter can only adapt an LR44 mechanically.

Battery PX14, 2.6v, 2.7v, 2.8V, 3v.....

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Battery PX14, 2.6v, 2.7v, 2.8V, 3v.....

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