Most electrochemical cells produce about 1.2 V to 1.8 V of electric potential. Different types vary slightly. A mercury cell has a voltage that is a little bit less than that of a zinc-carbon or alkaline cell. The voltage of a cell can also be affected by variables in the manufacturing process. Normally, this is not significant. Most consumer type dry cells can be assumed to produce 1.5 Vdc. There are certain types of cells whose voltages are predictable and exact. These are called standard cells. One example of a standard cell is the Weston cell. It produces 1.018 V at room temperature. This cell uses a solution of cadmium sulfate. The positive electrode is made from mercury sulfate, and the negative electrode is made using mercury and cadmium. When properly constructed and used at room temperature, the voltage of the Weston standard cell is always the same, and this allows it to be used as a dc voltage standard. There are other kinds of standard cells, but the Weston cell is the most common.
The cells you see in grocery, department, drug, and hardware stores that are popular for use in household convenience items like flashlights and transistor radios are usually of the zinc-carbon or alkaline variety. These provide 1.5 V and are available in sizes known as AAA (very small), AA (small), C (medium large), and D (large). You have probably seen all of these sizes hanging in packages on a pegboard. Batteries made from these cells are usually 6 V or 9 V. One type of cell and battery that has become
available recently, Zinc-carbon cells These cells have a fairly long shelf life. A cylindrical zinc-carbon cutaway diagram is shown at Fig. The zinc forms the case and is the negative electrode. A carbon rod serves as the positive electrode. The electrolyte is a paste of manganese dioxide and carbon. Zinc-carbon cells are inexpensive and are good at moderate temperatures, and
in applications where the current drain is moderate to high. They are not very good in extreme cold.
The alkaline cell uses granular zinc for the negative electrode, potassium hydroxide as the electrolyte, and a device called a polarizer as the positive electrode. The geometry of construction is similar to that of the zinc-carbon cell. An alkaline cell can work at lower temperatures than a zinc-carbon cell. It also lasts longer in most electronic devices, and is therefore preferred for use in transistor radios, calculators, and portable cassette players. Its shelf life is much longer than that of a zinc-carbon cell. As you might expect, it costs more.
Transistor batteries
Those little 9-V things with the funny connectors on top consist of six tiny zinc-carbon or alkaline cells in series. Each of the six cells supplies 1.5 V. Even though these batteries have more voltage than individual cells, the total energy available from them is less than that from a C cell or D cell. This is because the electrical energy that can be gotten from a cell or battery is directly proportional to the amount of chemical energy stored in it, and this, in turn, is a direct function of the volume (size) of the cell. C or D size cells have more volume than a transistor battery, and therefore contain more stored energy, assuming the same chemical type. The ampere-hour capacity of a transistor battery is very small. But transistor radios don’t need much current. These batteries are also used in other low-current electronic devices, such as remote-control garage-door openers, TV channel changers, remote video-cassette recorder (VCR) controls, and electronic calculators.
Lantern batteries
These get their name from the fact that they find much of their use in lanterns. These are the batteries with a good, solid mass so they last a long time. One type has spring contacts on the top. The other type has thumbscrew terminals. Besides keeping a lantern lit for awhile, these big batteries, usually rated at 6 V and consisting of four good-size zinc-carbon or alkaline cells, can provide enough energy to operate a low-power radio transceiver. Two of them in series make a 12-V battery that can power a 5-W CitizenBand (CB) or ham radio. They’re also good for scanner radio receivers in portable locations, for camping lamps, and for other medium-power needs.
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