The Hearing Aid Museum

Hearing Aids of all types—Ear Trumpets, Carbon Hearing Aids, Vacuum Tube Hearing Aids, Transistor Hearing Aids, Body Hearing Aids, Eyeglass Hearing Aids and much more!

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Click on the "General Information" button (top button above) for an overview and general information on this category of hearing aid.

Hearing Aid Batteries

No. 4 Mercury Hearing Aid "A" Battery

The No. 4 1.4 volt mercury hearing aid "A" battery was made by an unnamed manufacturer. It was used in vacuum tube hearing aids in the late 1940s and early 1950s. The No. 4 battery was the same size as the RM-4 battery manufactured by Mallory.

The No. 4 mercury battery (and the RM-4) were the largest "button" batteries made. It weighed 1½ oz. and measured ⅝" high by 1 3/16" in diameter.

Mercury batteries are no longer sold today because of the large quantities of mercury in them and the consequent environmental concerns.

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Bottom view of the No. 4 mercury hearing aid battery showing the model number (4) and the patent number. The bottom was the positive terminal (+) of the battery.

The small hole at the right was a pressure-relief valve that opened to relieve excess pressure that could be built up when the battery was being used.

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Side view of the No. 4 mercury hearing aid battery.

Learn more about this size of battery under the Mallory RM-4.

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