Miniature Cells and Batteries

In recent years, cells and batteries—especially cells—have become available in many different sizes and shapes besides the old cylindrical cells, transistor batteries, and lantern batteries. These are used in wristwatches, small cameras, and various microminiature electronic devices.

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Silver-Oxide Cells and Batteries

A silver-oxide cell is usually found in a buttonlike shape, and can fit inside a small wristwatch. These types of cells come in various sizes and thicknesses, all with similar appearances. They supply 1.5 V, and offer excellent energy storage for the weight. They also have a nearly flat discharge curve, like the one shown in the graph of above figure. Zinc-carbon and alkaline cells and batteries, in contrast, have current output that declines more steadily with time, as shown in following figure. This is known as a declining discharge curve.

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Silver-oxide cells can be stacked to make batteries. Several of these miniature cells, one on top of the other, can provide 6, 9, or even 12 V for a transistor radio or other light-duty electronic device. The resulting battery is about the size of an AAA cylindrical cell.

Mercury Cells and Batteries

A mercury cell, also called a mercuric-oxide cell, has properties similar to those of silver-oxide cells. They are manufactured in the same general form. The main difference, often not of significance, is a somewhat lower voltage per cell: 1.35 V. If six of these cells are stacked to make a battery, the resulting voltage will be about 8.1 V rather than 9 V. One additional cell can be added to the stack, yielding about 9.45 V.

There has been a decline in the popularity of mercury cells and batteries in recent years, because of the fact that mercury is toxic to humans and animals, even in trace amounts. When mercury cells and batteries are dead, they must be discarded. Eventually the mercury or mercuric oxide leaks into the soil and groundwater. Mercury pollution has become a significant concern throughout the world.

Lithium Cells and Batteries

Lithium cells gained popularity in the early 1980s. There are several variations in the chemical makeup of these cells; they all contain lithium, a light, highly reactive metal. Lithium cells can be made to supply 1.5 to 3.5 V, depending on the particular chemistry used. These cells, like silveroxide and mercury cells, can be stacked to make batteries.

The first application of lithium batteries was in memory backup for electronic microcomputers. Lithium cells and batteries have superior shelf life, and they can last for years in very-lowcurrent applications such as memory backup or the powering of a digital liquid crystal display (LCD) watch or clock. These cells also provide high energy capacity per unit volume or mass.