Alternative to PX625 battery

[Pieter12]

I just became aware of the Varta V80H rechargeable NiMH battery. It delivers 1.2-1.3 volts. Would it be suitable as a replacement for the mercury PX625, rated at 1.35 volts? Has anyone used these?

 

[pbromaghin]

PX625 battery is 1.5 volts, so no.

The guy who converted my Minolta SRT-201 circuits put in a Vinnic L1560. It died and Google gives several equivalents. I just today I ordered this off Prime:

Amazon.com

 

[ags2mikon]

Why not just use the mr-9 adapter and use a 357 silver oxide battery? I'm using them in a lot of my old junk and they work fine.

 

[Pieter12]

Both of those batteries are 1.5 volts. That won’t work for meters without recalibration. The PX625 is 1.35 volts, the V80 is closer at 1.2-1.3 volts. I am aware of the Wein zinc oxide batteries but they don’t last long.

 

[pbromaghin]

Oops. Senior moment. I both forgot and remembered that the conversion allowed mine to use 1.5 instead of 1.35. Never mind.

 

[mshchem]

I just switched to a non-meter prism on my F. Problem solved

 

[4season]

That NiMH cell might be worth a try, as NiMH maintains fairly constant voltage through much of it's discharge cycle.

But I was puzzled by how cameras designed for mercury batteries sometimes lacked any sort of on/off switch, save for the photocell itself. And one such camera in my collection (Konica S3) even has a "Mercury battery only" sticker. Curious, I queried Microsoft's AI, and it said that mercury batteries can "recover" somewhat, in a way that other battery types don't. And maybe that's the #1 reason why Konica didn't simply modify their meter to use 1.5 volt alkaline or silver batteries: Other battery types likely would need more frequent replacements, and customers would complain.

 

[reddesert]

I have not tried it so have no answer to the original question. It's not very expensive, considering, so interesting to try.

The genuine MR9 battery adapter contains a diode (probably a Schottky diode) to drop the 1.5v 357 battery to around 1.3v. The voltage drop would depend on current draw, but people who use these generally report good results.

Most of the original cameras using mercury batteries used a CdS photoresistor as the photosensitive element. These can have resistance of hundreds of kilo-ohms to several megohms in the dark. So depending on the meter circuit, if you stored your camera away with the lens cap on or in a dark environment, the current draw of the meter could be down to microamp levels, and the mercury battery would last a long time.

I think the cameras labeled "for mercury battery only" were related to the favorable discharge curve of the mercury battery (fairly constant voltage until it dies, unlike alkalines), under the assumption the average amateur user wasn't going to replace their batteries until obviously dead. Many cameras of that era didn't have a battery check indicator.

 

[Paul Howell]

I might give it a try, although 625 will be too large for my Konica ts which a take mercury 675 the zinc air 675 fits just fine. At the end of a shooting session I take the zinc air out and tape over the air holes. Topcon Uni also uses 675. Pentax Spotmatic does not matter much almost any battery will work. I have cardboard sleeves that I made for my Minolta 101 and 102 so I might try the rechargeable. One odd note, my Miranda EEs, the screw in battery compartment door is so tight I had to drill holes for the zinc air to breath.