What's the difference between a normal car battery and a deep-cycle battery?

A man checking his car battery. — A deep cycle battery is a lead acid battery designed to provide a steady amount of current over a long period. Jasmin Merdan / Getty Images

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 while keeping its voltage above 7.2 volts
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 a car battery is not designed to be totally discharged.

Originally Published: Apr 1, 2000

Lead-Acid Battery FAQ

What is in a lead-acid battery?

A lead-acid battery has a negative electrode made of spongy or porous lead and a positive electrode made of lead oxide. Both negative and positive electrodes are immersed in an electrolytic solution of sulphuric acid and water.

How do lead-acid batteries work?

Lead-acid batteries generate electricity through a double sulfate chemical reaction. Lead and lead dioxide on the negative and positive electrodes of a battery react with sulphuric acid in the electrolyte to form lead sulfate.

How long do lead-acid deep cycle batteries last?

Both car batteries, as well as deep cycle batteries, are lead-acid batteries that function the same way. Generally, the lifespan of lead-acid deep cycle batteries is about four to eight years.

How can you tell when your car battery is going bad?

Some clear signs that your car battery is going bad include a slower-than-normal starting engine, a clicking or cranking sound when you turn the key, intermittent sparks that cause your car to backfire.

Are lithium ion batteries deep cycle?

All lithium-ion batteries are deep cycle, which means that they are designed to be deeply discharged over and over again. Similarly, they can provide a steady amount of current over a long period of time.

What is the difference between a normal lead-acid car battery and a deep cycle battery?