Duracell No. 312 Zinc-Air Hearing Aid Battery
The Duracell No. 312 1.4 volt zinc-air hearing aid battery is pictured
at the right.
The No. 312 hearing aid battery came out by 1959 with the advent of
smaller behind-the-ear (BTE) and eyeglass hearing aids.
The first No. 312 batteries were mercury or silver-oxide batteries.
High silver prices
in the 1980s sounded the death-knell of the silver oxide battery,
coupled with the fact that the more modern silicon transistors could run
on the lower voltages supplied by the zinc-air batteries.
In 1977, in order to keep toxic mercury out of the environment,
zinc-air batteries began replacing the existing mercury batteries. Mercury batteries are no longer sold today because of their
high mercury content.
The batteries shown here are zinc-air
batteries, but the mercury and silver-oxide batteries looked identical except that the
zinc-air batteries had 2
tiny holes on the back that let the air in.
The No. 312 zinc-air battery battery measured 0.305" in diameter
by 0.135" thick. |
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The bottom (positive end) of the No. 312 battery. Note the two little air holes
(yellow dots at the ends of the vertical "+" arms). A brown tab seals these holes keeping the air
out until the battery is ready to be used. By doing this, zinc-air
batteries have a long shelf life. When the tab is removed, the battery
starts "working" and even if you don't use it, in a few weeks it will be
dead.
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The Duracell zinc-air batteries typically came either 4 or 8
batteries to a pack. This is an 8-pack. Notice that No. 312 batteries
have brown tabs on them, making it easy to identify them.
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Top view of the No. 312 zinc-air hearing aid battery showing its size.
(Each mark on the ruler is 1/16".) |
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Relative size of the five sizes of zinc-air hearing aid batteries as
seen from the top. From left to right they are battery numbers 5, 10,
312, 13 and 675. |
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A three-quarter view of the 5 zinc-air hearing aid batteries showing
their relative size. From left to right they are battery numbers 5, 10,
312, 13 and 675. |
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Side view of the 5 zinc-air hearing aid batteries showing their
differences in height. From left to right they are battery numbers 5,
10, 312, 13 and 675. |
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Bottom view of the 5 sizes of zinc-air batteries showing the
color-coded tabs that seal the air holes before they are used. From left
to right they are battery numbers 5 (red tab), 10 (yellow tab), 312
(brown tab), 13 (orange tab) and 675 (blue tab).
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