Battery Question

Adam W

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Hi Folks,

I just bought a camera (Minolta Hi-Matic 7sII) that originally took an EPX675 mercury cell. What is a long lasting substitute? I know the voltage might be slightly off--that's okay. I just don't want a short-lived zinc-air like the Wein.

Thanks!
 

E. von Hoegh

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A 675 zinc air cell. Go to the local hardware, and purchase an O ring to keep it central. Daub all but one airholes with nail lacquer, it will last for about one year.
 

beemermark

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Just get a 625 Alkaline battery. It'll be close enough for B&W and Color film and will last a long time. When you put it in the camera check it with the sunny 16 rule and if necessary (very doubtful) adjust the ISO to make the exposure correct. Down the road do the same sunny 16 rule to see if the battery depletion is changing you setting. No sense spending a lot of money on a short lived battery or expensive adapter when a cheap battery will work 95% of the time. People really over think this.
 

MattKing

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beemermark

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MattKing said:
That will be too large if the camera originally took a 675 battery.
Click to expand...
Are you sure? Way too many battery sizes and I used to own a Minolta 7 but I thought the 625 was a physically same size replacement. I have it in a number of cameras (including Leicaflex's) that originally took the largish mercury batteries. Always willing to stand corrected.
 

MattKing

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The size 675 battery is a button cell type battery with physical dimensions of a diameter of 11.6 mm and a height of 5.4 mm.
The size 625 battery is a button cell type battery with physical dimensions of a diameter of 15.5 mm and a height of 5.9 mm.
 

reddesert

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The PX675 is a button cell that is cylindrical and doesn't have an overhanging flange like the PX625. The PX675 is about the same size as the common LR44/SR44/357 battery available in alkaline (LR44) and silver oxide (SR44) if you aren't worried about the voltage difference. That will probably fit, but if it doesn't there are watch/battery cells available in many sizes about the same diameter and smaller thickness (eg a 386 cell is about a millimeter thinner than a 357).
 

CMoore

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Is there any kind of list or chart that cross references some of these battery questions.?
Thank You

If there were, i suppose it would already be a sticky............
 

Paul Howell

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I have the hi mate as well and use a hearing aid battery, last a couple of months, after each use you can remove the battery and tape over the vents on the back of the battery and it will last a bit longer. Some cameras like my Miranda EE have a very tight fit of the screw in cap for the battery and I had to drill a small hole in it so there is enough air to power the battery. And as noted above an O ring is helpful, some folks cut out strips of cardboard to shim the battery.
 

ags2mikon

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My vote is for the 675 air/zinc cell. I get mine at Walmart and seal all the holes but 1. Here in dry NM i get about 6-9 months out of them. The voltage is right and everything works properly.
 

Huss

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ags2mikon said:
My vote is for the 675 air/zinc cell. I get mine at Walmart and seal all the holes but 1. Here in dry NM i get about 6-9 months out of them. The voltage is right and everything works properly.
Click to expand...

How long do you let it breathe before you seal up the holes? It needs air to activate it/bring it up to the correct voltage, no?
 

ags2mikon

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I pull the tape off and while I am loading the film backs and loading the truck one last trip to the restroom and they are ready. 15-30 minutes. I used to pull the tape and then re tape them but it is too easy to loose the tape. They are so cheep if I only got 1 use i'd be okay with it. The only other option is to use the MR-9 adapters. I have converted some like that. My Nikon F cameras never worked right with the MR-9 adapters.
 
OP
OP

Adam W

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Well, now I feel a bit foolish.

The camera arrived and it's a Minolta Hi-Matic 7s, not the 7sII. It doesn't take a 675, it takes the 625, for which I already have a substitute. Thanks anyway for all your responses.

Adam
 

E. von Hoegh

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Huss said:
How long do you let it breathe before you seal up the holes? It needs air to activate it/bring it up to the correct voltage, no?
Click to expand...
You seal all but one hole. I use them primarily in Nikons/Nikkormats, but also a couple others and recently a Canon FTb. Cameras like the Spotmatics with a bridge circuit will work accurately with silver oxide cells, bridge circuits are relatively insensitive to a few tenths of a volt difference.
 

Donald Qualls

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ags2mikon said:
My Nikon F cameras never worked right with the MR-9 adapters.
Click to expand...

Some voltage adapters won't pass enough current to operate camera circuits on the high-drain end of button cell usage. I have an adapter to use a small lithium cell in my Pentax 1/21 Spotmeter, and it won't pass enough current to light the dial light. Eventually I'll (pay someone to) either install a secondary battery holder for a silver oxide cell to run the dial light, or a regulator to run that off the 9V booster battery.
 

ags2mikon

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Yes, Donald you are spot on. The Nikon F photomic heads needed 2 cells to operate and had a short life compared to other cameras at the time with only 1 battery. I think that the MR-9 adapters were just a small diode that created a small voltage drop to make the silver oxide batteries close to 1.35 volts. I have wired small schottky diodes into some meters to replicate the mr-9. One was my Horseman film plane light meter. I sure miss radio shack.
 

E. von Hoegh

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It's very easy to recalibrate the F heads, even the battery check. Then use S76/LR44 cells with an O-ring to keep them centered. Otherwise, the air cells work well with all but one airhole blocked. I've had poor results with the adapters too.
 

BobUK

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The above link takes you to an extensive article titled

"The Mercury Cell Problem and its Solution."

Using the information on this site I have made quite a few adaptors, and also fitted diodes inside a couple of cameras to get around the mercury cell problem.

If you do add a diode in the camera battery circuit, remember to stick a note under the camera telling you and the next owner what size battery to fit in the future.


Whoever put this article together deserves a round of applause, as not only is it very comprehensive, but easy to understand.
 

murdockhendrix

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I've corresponded with Frans de Gruijter, the author of the paper, back in 2020. I had a couple of Olympus cameras (35RC and the 35SP) I wanted to use again. My soldering skills are as good as my piano playing skills, non-existent. SO I purchased a couple of adapters from him and have been very happy with them and the ability to shoot my old cameras.
 

Pieter12

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Not cheap, but you can buy an adapter that fits a silver 386 battery and lowers its output to 1.35 volts. It is slightly deeper than the mercury battery and that may be an issue with certain equipment. It works fine on my Leica M5 and CL.
 

beemermark

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Too many internet experts with not enough knowledge with enough cameras. Many cameras have an electrical Rosette bridge that will compensate for voltage loss and sometimes higher that the voltage of a current battery over the mercury. Some meters (like the Leica M4-R) will allow an adjustment to compensate for the higher voltage and work fine with the voltage drop. Only one way too find out - buy a cheap current battery and test it. I have a whole lot of cameras, some work fine, some are adjustable and some need an expensive adapter. Recently picked up two Chinons that use a mercury battery and both work fine with a 625 battery. Buy a cheap battery and test it.
 
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