<p>A battery converts chemical energy into electrical energy by a
chemical reaction. Usually the chemicals are kept inside the battery. It
is used in a circuit to power other components. A battery produces
direct current (DC) electricity (electricity that flows in one
direction, and does not switch back and forth).</p>
<p>Using the electricity from an outlet in a building is cheaper and
more efficient, but a battery can provide electricity in areas that do
not have electric power distribution. It is also useful for things that
move, such as electric vehicles and mobile phones.</p>
<p>Batteries may be primary or secondary. The primary is thrown away
when it can no longer provide electricity. The secondary can be
recharged and reused.</p>
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