Zerad Hearing Aid Battery Tester
This dual-scale battery meter carries the Zerad name. It was one type
of battery meter used in the mid to late 1940s and early 1950s to test the voltages of
both "A" and "B" batteries
of one-piece hearing aids that were produced from about 1947 to 1952.
Incidentally, the name "Zerad" is a contraction of the name Zenith
Radio Corporation ("ZE"nith "RAD"io), the makers of the very popular
Zenith hearing aids of the day.
The wires of the 3 probes were color-coded for ease of use. When testing
batteries, you held the black-wired probe is the negative side of the battery,
and touched one of the other probes to the positive side. The red-wired probe
was for testing "B" batteries and the yellow-wired probe for testing "A"
batteries.
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