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People who have recreational vehicles (RVs) and
boats are familiar with deep cycle batteries. These batteries are also
common in golf carts and large solar
power systems (the sun produces power during the day and the
batteries store some of the power for use at night). If you have read the
article How Emergency Power Systems Work, then you
also know that an alternative to gasoline-powered generators is an inverter
powered by one or more deep cycle batteries.
Both car batteries and deep cycle batteries
are lead-acid batteries that use exactly the same chemistry for
their operation (see How Batteries Work for more information).
The difference is in the way that the batteries optimize their
design:
·
A car's battery is designed to provide a very large amount
of current for a short period of time. This surge of current is needed to
turn the engine over during
starting. Once the engine starts, the alternator provides all the power
that the car needs, so a car battery may go through its entire life without
ever being drained more than 20 percent of its total capacity. Used in this
way, a car battery can last a number of years. To achieve a large amount of
current, a car battery uses thin plates in order to increase its surface
area.
·
A deep cycle battery is designed to provide a steady amount
of current over a long period of time. A deep cycle battery can provide a
surge when needed, but nothing like the surge a car battery can. A deep
cycle battery is also designed to be deeply discharged over and over again
(something that would ruin a car battery very quickly). To accomplish this,
a deep cycle battery uses thicker plates.
A car battery typically has two ratings:
·
CCA (Cold Cranking Amps) - The number of amps that the
battery can produce at 32 degrees F (0 degrees C) for 30 seconds
·
RC (Reserve Capacity) - The number of minutes that the battery
can deliver 25 amps while keeping its voltage above 10.5 volts
Typically, a deep cycle battery will have two or three times
the RC of a car battery, but will deliver one-half or three-quarters the
CCAs. In addition, a deep cycle battery can withstand several hundred total
discharge/recharge cycles, while car batteries are not designed to be
totally discharged.
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