Confused about 675 to 625 mercury battery modification

[saman13]

So, I have a Minolta 7S that takes the old 625 battery. When I first bought the camera I bought a WeinCell battery to use (expensive). I've been doing my research and from what I gathered, these batteries are nothing more than a 675 battery with a metal washer around it. I also read that an easy fix to be able to use these cheaper 675 batteries is to buy a #9 O-ring, place it around the smaller battery, and it would be a perfect fit.

This made sense as far as the fit goes, but what didn't make sense to me is that rubber is an insulator and I thought that these cameras took their ground voltage from the side of the battery (that is now insulated). But I bit the bullet anyway and paid the whopping 30 cents for an O-ring, placed it around a battery and popped it into my camera. Perfect fit, but as I suspected the meter will not work because the battery is insulated from the top and edges of the battery chamber.

Now, I know that I can take the washer off the WeinCell and use it on a new battery but I have 2 cameras and 1 WeinCell. Is there a correct size metal washer that I can use for the other camera?

Second question: are there cameras with battery compartments that can make contact with the negative terminal of the battery when the sides are insulated? Or, more importantly to me, can the Gossen Luna-Pro light meters (or other older mercury battery-taking light meters) operate with these O-rings instead of a metal washer?

Thanks for the help!

 

[BAC1967]

Some cameras have a battery cover that will make contact with battery, some don't. You could just shove a little tin foil in between the batter and the side of the battery chamber. I would leave the O-ring in place to hold the battery in the center. I have filled the gap with just tin foil but you do run the risk of shorting out the battery if it touches the wrong parts in the battery compartment. The O-ring will help prevent that.

 

[E. von Hoegh]

Make a "C" out of #12 bare copper wire to take the place of the o-ring. If you block off all but one of the airholes the zinc air cells last far longer. I had one last over two years in a Nikkormat.

 

[mklw1954]

These adapters work great - http://www.paulbg.com/Nikon_F_meter_batteries.htm

I use one with my 7S and other cameras that use the 675 batteries. When not in use, remove the battery and cover the + side with the original tab or scotch tape and the battery will last.

 

[Dan Fromm]

Metal rings that fit 675 cells are offered on eBay. See my discussion of them at http://www.galerie-photo.com/horseman-4x5-exposure-meter.html