Acousticon No. 2B Hearing Aid Battery

The Acousticon No. 2B,  1½ and 3 volt  battery was used in some carbon hearing aids from around the mid 1920s through the 1930s.

It weighed 6¼ oz., and measured 2" by 1" by 3⅞" high.

The positive terminal (labeled "+" - left) was larger than the other two, so you couldn't plug things in backwards, thus preserving the correct polarity.

The negative terminals are labeled -1½ volts (upper) and -3 volts (lower).

Presumably, if you didn't need all the power available, you could plug into the 1½ volt socket. If you needed more power, you plugged into the 3 volt socket and had increased volume.

However, there are a couple of mysteries associated with this battery. First, carbon hearing aids typically used either 3 volt or 4½ volts, not 1½ volts. Second, since the two cells had to be wired in series (to get the 3 volts), if you used the 1½ volt connection, you'd use up the first cell, and would thus waste the second cell as you could not access it for the second 1½ volts, and if the first cell was used up, then plugging into the 3 volt connection would only give you somewhat less than 1½ volts, not 3 volts.

The only other battery of which I know, that used this two-voltage arrangement, was the Fred Ring No. 3 battery that was also used with Acousticon carbon hearing aids.
 

Close up of the Acousticon No. 2B battery showing the model number (center).

The inscription around the top reads, "Acousticon Grand Prize Battery/Super Duty Type No. 2B Made in USA."

Down one side it reads, "Dictograph Products Co. Inc./Registered US Patent Office" and down the other side, "Gold Medal Liege 1930/Exposition Internationale".

Another mystery: this battery's internal wiring is such that if you used up the first cell, you basically had to waste the second cell. This begs the question, "Why did this battery win a prize?" Obviously, we're missing something.