Acousticon 57 Hearing Aid Battery This is an Acousticon 57 "Double Duty" battery that was used in some Acousticon carbon hearing aids." Most carbon hearing aids used either 3 or 4˝ volts batteries—but this one has 4 cells. Therefore, the question is what they meant by "double duty". Either it was wired in series for 6 volts , or in series-parallel for 3 volts with double the capacity. It weighed 1 pound, 1 oz., and measured 4" by 1" by 3⅞" high. |  | Click picture for larger view | | | | | | |
