No. 4Z Mercury Hearing Aid "A" Battery
The 4Z 1.4 volt mercury hearing aid "A" battery was made by
an unnamed battery manufacturer. It was used in a few vacuum
tube hearing aids manufactured around 1947 and 1948.
This battery was extremely rare and, as far as I know at this point,
was only used in the Acousticon A-90 and in some A-90M vacuum tube
It was the same diameter as the RM-4 but was not as high.
The 4Z battery weighed 1.1 oz. compared to the RM-4 at 1.5 oz.
It measured ˝" high by 1 3/16" in diameter as compared to the RM-4 at