Archived posting to the Leica Users Group, 1997/02/10
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]About batteries ... as far as I know, Varta still makes and supplies mercury batteries. When I was in Germany last year there were fresh boxes just received at the photo shops and no word that there would be any restriction. A German list-member reported the same a few days ago. People have also pointed out that there are form- and fit-equivalent batteries that have different function, but don't seem clear about the differences. Mercury (Zn-HgO) batteries have a very constant, exactly 1.34 volt output. Over the course of aging, and with load and differing temperatures, this might drop to 1.3 volts. When it's worn out, the voltage drops off sharply. This sort of stability is ideal for light meters. Most of the look-alike batteries are alkaline (Mg-MnO2) which start out at 1.8 volts or so and drop to 1.4 or so with aging. You can put a 625U in place of a PX625 in a Leicameter C for instance, and initially it will read about 1 stop high (you can check this with the battery-check function) and will degrade through time to about 1 stop low. The other primary cell that's useful for light meters is zinc-air, commonly used in hearing aids. They are much closer to mercury in initial voltage (1.45 volts nominal) but vary more with time and temperature, as I recall. There is a company (Wein) that makes a line of light meter batteries that are zinc-air cells in a plastic housing that makes them the same size as the mercury batteries were. If you use one of these, make sure you check with your light meter's battery check function to be sure that it's within the usable range. Some cameras use a PX27 battery which was originally 3 mercury cells in series; there is no alkaline equivalent. But Minox makes a replacement that uses 3 zinc-air batteries in a tube, and you can replace the zinc-air cells yourself. (http://www.minoxlab.com) Another alternative is to have the meter recalibrated for use with an alkaline battery. You will have to replace the battery more often than with the mercury cell because alkaline cells drift more, but at least you can buy them in the US. In the meantime, be sure your friends visiting Europe or Asia bring back batteries for you... - -- David Josephson / Josephson Engineering / San Jose CA / david@josephson.com