Batteries generate direct current (DC) electricity through reactions between chemicals and metals. Different battery formulations, such as lead-acid, carbon-zinc and lithium-ion cater to a variety of applications. Every battery has both voltage and amperage ratings that help you determine its suitability for a given device.
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A battery consists of one or more cells connected together. The cell contains chemicals and metal plates that produce electricity. The chemicals determine whether the battery is a disposable type, such as a carbon-zinc battery, or a rechargeable battery, such as one that uses lead-acid chemistry. The cell’s chemistry also determines its voltage. For example, nickel metal hydride cells produce about 1.2 volts, whereas an alkaline cell makes 1.5 volts.
A battery’s total voltage comes from adding the voltages of each of its component cells. For example, a 6-volt lantern battery has the same alkaline cell chemistry as a “D” cell’s, but has four times the voltage. The lantern battery has 4 internal cells of 1.5 volts each for a total of 6 volts. Though devices use both voltage and current, voltage is the more critical parameter; electronic circuits in particular are sensitive to voltage.
Electrical current is measured in amperes, usually abbreviated to amps. If you compare electricity to water flowing in a pipe, the voltage is like the water’s pressure and the current is the amount of water. The more power a device needs, the more current it draws, and the faster it drains the battery. A pocket radio uses a fraction of an amp of current, a battery-powered lawn edger needs a few amps, and your car’s starter takes hundreds of amps.
A battery’s capacity is rated in amp-hours, or how many amps of current it can produce for a number of hours before it weakens. A 10 amp-hour battery can supply 1 amp of current for 10 hours, 2 amps for 5 hours or a quarter amp for 40 hours. A battery’s bulk generally determines its amp-hour rating: Larger batteries tend to have more amp-hours than small ones.
Battery-powered devices have current and voltage requirements in their specifications. As long as a battery meets the voltage rating, it will power the device. It will draw as much or as little current as it needs, regardless of the battery’s size. A large battery with a generous amp-hour rating will power the device longer than a small battery.
Two batteries of the same size and different chemistries will have different voltages. The reduced voltage from a nickel metal hydride battery versus an alkaline type may affect the performance of electronic devices.