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Author Message   Charlie Tinkerer Username: Charlie Post Number: 180 Registered: 07-2006 Rating: N/A Votes: 0 Posted on Thursday, September 25, 2008 - 09:29 am:    #675 zinc/air hearing aid batteries are cheap, carried in most pharmacies and put out a stable 1.4 volts. They are slightly smaller than the mercury batteries and may need to be shimmed with a wad of aluminum foil. No recalibration necessary.