Mallory RM-4 Mercury Hearing Aid "A" Battery
The Mallory RM-4 1.4 volt mercury hearing aid "A" battery was
manufactured by the Mallory Battery Co in the USA. It was used in
vacuum tube hearing aids in the late 1940s and early 1950s.
The RM-4 mercury battery was the largest "button" battery made
for use in hearing aids. It weighed 1˝ 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 Mallory RM-4 mercury hearing aid battery showing the
manufacturer and model number. The hole in the center was a
pressure-relief valve that opened to relieve excess pressure that could
be built up when the battery was being used.
The bottom was the positive terminal of the battery. |
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Side view of the Mallory RM-4 mercury hearing aid battery. |
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The Mallory RM-4 mercury hearing aid battery was the largest button
battery used in hearing aids. Here you can see it contrasted with the
smallest hearing aid battery used—the tiny No. 5
battery (right). |
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Button batteries got smaller as the years went by. This picture shows
the progression of button batteries from the largest to the smallest as
seen from the side. They are from the left, the RM-4, RM-3, RM-1, 625.
675, 13, 312, 10 and 5. This is by no means all the button batteries
made—just a sampling of the various sizes. |
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The progression of button batteries from the largest to the smallest
as seen from the top.
They are from the left, the RM-4, RM-3, RM-1, 625. 675, 13, 312, 10 and
5. |
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The picture at the right shows the three sizes of the RM series of mercury batteries. From left
to right they are the RM-4, RM-3 and RM-1. There doesn’t appear to have
been an RM-2 battery used in hearing aids.
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