Mercury battery

Mercury batteries were used in the shape of button cells for watches, hearing aids, cameras and calculators, and in larger forms for other applications.

For a time during and after World War II, batteries made with mercury became a popular power source for portable electronic devices.

After the Second World War the battery system was widely applied for small electronic devices such as cardiac pacemakers and hearing aids.

Mercury oxide batteries were made in a range of sizes from miniature button cells used for hearing aids and electric wrist watches, cylindrical types used for portable electronic apparatus, rectangular batteries used for transistor radios,[5] and large multicell packs used for industrial applications such as radio remote control for overhead crane systems.

Sodium hydroxide cells have nearly constant voltage at low discharge currents, making them ideal for hearing aids, calculators, and electronic watches.

When reaching the end of its life, this smaller cell would discharge first causing the battery terminal voltage to drop sharply by 0.9 volts.

This provided a very predictable and repeatable way to warn users the battery needed replacement while the larger capacity cells kept the unit functioning normally.

[7] Mercury batteries with cathodes made of a mix of mercuric oxide and manganese dioxide have output voltage of 1.4 V and a more sloped discharge curve.

[8][9] The ban on sale of mercury oxide batteries caused numerous problems for photographers, whose equipment frequently relied on their advantageous discharge curves and long lifetime.