What battery should I use in my Hi-Matic 7s?

[ElectroWNED]

I've been told 10 different things by 10 different people.

a few numbers/words running through my head: 675, 625, MR9, Wein cell, silver oxide, vinc air... :bang:


What battery is going to last a while and not cost $$$?

 

[Bassism]

The original battery for the 7s is the PX625 mercury cell, which is no longer available.

What I use in mine are hearing aid batteries. They should be available at any department store or whatnot and they come in a pack of 6 for somewhere around 8 bucks I think. These are zinc-air batteries like the Wein cells, but at a much lower cost. The only downside is that they have a limited life of a few months. However, they are the correct voltage and will give accurate metering. I'm not sure what the model number of these batteries is, but I think they list them on the back as being a replacement for the PX625.

The cheaper solution is to use an SR44 with a bit of tin foil or something to make up the size difference. This will last essentially forever and will be cheaper, but your meter won't be accurate and you'll have to do some experimenting to figure out what the effects on the meter are and test it periodically for changes as the voltage in the cell drops.

The zinc air batteries hold the right voltage and stay at about the same level until they burn out, so they are the easier, more dependable choice.

 

[Bill58]

I use the Kanto/ C.R.I.S. MR-9 adapter w/ a SR43 or V386 battery. Works fine for me.

 

[ElectroWNED]

alright, I'm gonna get the 675 hearing aid batteries (1.5v) and stock up.

 

[ElectroWNED]

Bought a 6 pack, popped one in, and the meter just goes to 13 (EV meter) and doesn't really move much. I shot a roll fully manual and I got a little more than a handful of proper exposures... I've got a handle on aperture, but shutter speed is more difficult.

Anybody need some 675's :\

 

[racoll]

Since the original battery was a 625 battery, why not try a Wein Cell 625? I use those in mine with great success.

 

[bobdole369]

The Hi-matic 7s I just purchased has a PX625A battery that is working. However i tested and the voltage is 1.5V. Also my images are coming out about a stop or two overexposed. I suppose I can just adjust 1 EV number down, but the tinkerer in me thinks I need a circuit to drop it to 1.35V.

 

[FallisPhoto]

The Hi-Matic 7S used a PX625 (mercury) battery. You can't get those anymore. Most of the drop-in replacement batteries in 625 size have the wrong voltage (1.5 volts instead of 1.35 volts) and will give you inaccurate exposures. The one exception is the Wein cell, which starts off at 1.4 volts, then very quickly drops to 1.35 volts and stays there. However, they are not cheap. Here's my solution, that I reached after years of doing this:

1. Buy a 625A (alkaline) battery and tape a wire to both ends so it discharges for 24 hours.
2. Look closely at the battery. You will notice that a replacement 625A battery is actually a smaller battery that has been force-fit into a metal shell. These can be 675 batteries or 386 batteries. It is that 625-sized shell that you want to save and you want the kind that uses a 675 battery in the center.
3. Remove the battery from the shell. Wear eye protection and rubber gloves, because the stuff inside an alkaline cell is corrosive and you will probably have to take it out in pieces.
4. Once you have it out, drill a 1/8 inch hole in the bottom of the shell. This hole will allow air to get to the battery you are going to put in there and will be used to poke the fresh battery out of the shell when it is used up.
5. You can use the shell as an adapter for #675 hearing aid batteries, which are the right voltage and only cost about $1 each. Buy some of those, stick one in it and put it in the camera.

Edit: Of several methods for powering the camera with the right voltage, that's the cheapest I know of that is elegant, will work right and won't require modifying the camera.