Minolta SRT 101 Hearing Aid Battery Use Questions

[alex_diaz]

I just came into the possesion of a Minolta SRT101 and want to make sure it

functions properly before investing in Wein cells or adapters. If the voltage of

a hearing aid battery is +.15 volts what adjustments would be most common to

compensate for this change in current? Should I change the selected ISO or

adjust shutter speed? Should I just experiment with different settings and take

notes? Are there any "better" hearing aid batteries to use than others? Any

advice would be much appreciated. Thanks

[richard_oleson]

A hearing aid battery is not +.15 volts. It's more like +.05 volts, which is almost always close enough for photographic purposes. For this voltage match you need a Zinc/Air cell, which is what the hearing aid batteries are.

 

A silver cell will be +.15 - +.20 volts, which may be enough to cause underexposure, and an alkaline cell will start out at +.15 and drift down over time to -.35 or more ... which will give you exposures all over the map, some of which will be good and may fool you into thinking it works okay.

[richard_oleson]

Sorry, I should have mentioned: you can use a silver cell if you buy a CRIS adapter for it. The adapter includes circuitry to drop the voltage down to the proper level.

[walter_degroot]

COUPLE OF THINGS DON'T BUY A 12 PACK. HEARINGT AID CELLS WILL DRY OUT AND likely DIE IN LESS THAN 2 YEARS EVEN WHEN still sealed.

you can also coat two of the 4 holes with nail polish or crazy glue.

they look more like tiny dents.

this will slow down the drying-out process.

about 4-6 months life in pennsylvania

probably less in a dryer climate.with a match pointer type camera. where the meter circuit doesn't do any hard work. too bad the larger flanged cells like the ones in the canonet arent made in hearing aid type.

 

enjoy your old camera it and others like it can still take many excellent photos. and don't look like plasit toys as newer cameras do.

[david_m]

Hearing aid cells have a much longer life than that provided they remain sealed. The expiration date is usually printed on the package and is several years.

[leicaglow]

Also, in some cameras, if the voltage is slightly different, the exposure meter can be off.

[charles_stobbs3]

The #675 hearing aid batteries are 1.40 volts. I believe the old mercury batteries were 1.35 volts. Not enough difference to warrent recalibration even with slide film. I just bought a CVS 8 pack with a 2009 use by date.

[richard_oleson]

I'll second Charles on the voltage issue; there may be exceptions, but my experience with the 1.4 volt cells has been excellent. I think it's actually more stable and closer to the 1.35v target than you get with circuit modifications such as the CRIS adapter and silver cells. But either approach, I believe, will give perfectly adequate results.

[john_shriver]

Hearing aid cells are VERY close to the mercury cells. They really have the same chemistry: zinc and oxygen. The difference is that the hearing aid cells get the oxygen from the air (through the holes), where the mercury cells got it from the breakdown of mercuric oxide. The mercury was not part of the electrochemistry of the cell. Yeah, the nominal voltage of the mercury cell was 1.35 volts, and the zinc-air cells are nominally 1.4 volts, but they're really closer than that.

 

You can just as easily test the camera with a alkaline 625 cell, just don't be surprised if the readings are off by a stop one way or the other. Although the hearing aid 675's are probably easier to find, and cheaper. But you will need that o-ring and may need a spacer washer.

 

The most important thing about the hearing aid batteries is "REMOVE WHEN NOT IN USE". They aren't sealed, and are much more likely to keep reacting (zinc is very reactive) and eat your camera for dinner...