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 HSW article entitled 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 the way that the batteries optimize their design:
A car battery tytpically has two ratings: CCA (Cold Cranking Amps) and RC (Reserve Capacity). CCA is the number of amps that the battery can produce at 0 degrees F for 30 seconds. Reserve capacity is the number of minutes that the battery can deliver 25 amps while keeping its voltage above 10.5 volts. Typically a deep discharge battery will have 2 or 3 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 a car battery is not designed to be totally discharged.
- 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% 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 instead 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.
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