What Is a Deep Cycle Battery, and How Does It Differ From a Standard One?

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

Deep cycle batteries and standard lead-acid batteries are both pivotal in the world of energy storage, powering everything from vehicles to renewable energy systems. Despite their similarities, these battery types serve distinct roles, tailored to different applications due to their unique characteristics.

So, what is a deep cycle battery? A subtype of lead-acid batteries, they are designed to be regularly deeply discharged using most of their capacity. Unlike standard lead-acid batteries, which are optimized for short, high-current bursts of energy (like starting an engine), deep cycle batteries are built to provide a steady amount of power over a long period.


In this article, we'll explore the difference between deep cycle and standard lead-acid batteries. In the process, consumers can select the right battery for their specific needs. We'll also explain how deep cycle batteries achieve these cyclic charges without degrading significantly.

How Much Power Are We Talking About?

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.


The Role and Power of Starter Batteries

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 lead plates in order to increase its surface area.


Deep Discharge Battery Capacity

Most deep cycle batteries are designed to provide steady amounts 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 deep discharge, a deep cycle battery uses thicker lead plates.


What Are Flooded Deep Cycle Batteries?

Flooded deep cycle batteries, also known as wet cell batteries, are a type of lead-acid battery designed for applications that require a steady and reliable power supply over an extended period. The "flooded" descriptor comes from the fact that these batteries contain liquid electrolyte (a mixture of water and sulfuric acid) that freely floods the internal components, covering the lead plates within the battery cells.

This design allows for the efficient exchange of ions between the plates during the charge and discharge cycles, making them well-suited for applications such as marine use, recreational vehicles, solar power storage, and backup power systems.


However, because the electrolyte is in liquid form, flooded deep cycle batteries require regular maintenance. This includes checking the electrolyte level and adding distilled water as necessary to compensate for evaporation and the electrolysis process that occurs during charging.

While they are generally more affordable than their sealed counterparts (AGM batteries or gel batteries), the need for maintenance and the risk of spillage or leakage of the acidic electrolyte are significant considerations when choosing a battery for a specific application.


Battery Ratings

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 standard car battery type, 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.


Battery Charger Needs

For standard car batteries, which are typically lead-acid types, a charger that can deliver a constant current is necessary. These batteries are designed for short, high-current bursts to start the engine and not for prolonged discharges.

A smart charger is highly recommended because it can adjust the charging rate based on the battery's state, preventing overcharging and extending the battery's lifespan. Smart chargers often come with multiple charging modes, including a maintenance or trickle charge option, which is ideal for keeping a battery topped off without causing damage over long periods of inactivity.


Deep cycle batteries, on the other hand, require a charger that includes features like adjustable charge rates to accommodate the slower absorption rate of deep cycle batteries and the ability to deliver a consistent, low current for extended periods. Some chargers are designed with deep cycle batteries in mind, offering settings that help condition the battery, extend its life, and ensure it is charged efficiently and safely.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.


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.