Hearing Aid batteries
Hearing aids are designed to be small and light so that they can be worn
behind, or even in the ear. Of course, they still need a suitable source
of electricity to function. Hearing aid batteries have thus been optimized
to be small and light.
The battery technology best suited to produce light batteries is the zinc
air battery. Out of all of the battery chemicals commonly in use today,
it allows for the greatest amount of power to be stored for a given weight.
This is a function of using air (or more precisely the oxygen in the air)
as part of the chemical process to produce electricity. Because no storage
is required for this chemical inside the battery, it can be made lighter.
This unique technology brings a few features of its own. Zinc are batteries
are sealed when manufactured. While sealed, they have an exceptionally long
shelf life. To use a zinc air battery, you have to remove the sealing tab
from tiny holes on the battery to let in air. This starts the electricity
producing chemical reaction. The way this chemical process proceeds makes
it ideal to provide a steady current over a period of time. Zinc air batteries
are not good at producing peak power quickly in a high drain application
(e.g. a camera), because of the steady rate of the chemical process.
In hearing aids, this steady discharge is exactly what's required, however.
Because the chemical process continues even when the battery is not used
to power a device, the shelf life of a zinc air battery once un-sealed is
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