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What is a deep-cycle battery?

Power - by Joe Weber - updated on 4/9/2024

Marine deep cycle battery with a battery tester on a counter

Deep-cycle batteries are designed to be repeatedly discharged and recharged. They are commonly seen in golf carts, RVs, boats and more. Keep reading to learn all there is to know about this highly useful battery.

What Are Deep-Cycle Batteries?

To the untrained eye, deep-cycle batteries may look identical to car batteries, but in reality, they are very different. Unlike car batteries, deep-cycle batteries are specifically designed to deliver sustained power over extended periods, maintaining reliable operation until they are discharged by 80% or more, at which point they require recharging. This can be done over and over throughout the life of the battery.

It is important to keep in mind that while deep cycle batteries can withstand up to 80% depth of discharge (DoD) It's important to note that most manufacturers advise against going more than 50% to maximize the battery's lifespan.

Components of A Deep-Cycle Battery

Starting (cranking) batteries share many similarities with deep-cycle batteries. Deep-cycle battery construction is essentially the same. They both have:

  • Lead plates: This is the active part of the battery. The lead plates react with the electrolyte to produce electricity.
  • Electrolyte: The electrolyte is a mixture of sulfuric acid and water. It conducts electricity and helps to carry the chemical reaction between the lead plates. It comes in many forms, liquid (flooded), Absorbed Glass Mat (AGM) and Gel.
  • Case: The case is the outer shell that protects the battery from damage and holds the other components in place.

So, How Are Deep-Cycle Batteries Different?

The thing that makes deep-cycle batteries "deep-cycle batteries" is that they are made with much thicker lead plates than traditional lead-acid batteries.

These thicker plates allow deep-cycle batteries to be discharged and recharged over and over with minimal wear and tear.

Cold Cranking Amps vs. Reserve Capacity

Most of us are pretty comfortable with shopping for car batteries. One of the things you look for in a car battery is how powerful the battery is so you can start your car in the cold winter. This number is called the Cold Cranking Amps or CCA.

For deep-cycle batteries, things are a little different. The specification that is more important when looking at your different options is referred to as the Reserve Capacity or RC.

The technical details:

  • CCA refers to the number of amps a battery produces in 30 seconds at 0°C (32°F).
  • RC refers to the number of minutes a battery can produce 25 amps.

Because the whole purpose of a deep-cycle battery is to power equipment for long periods over and over, reserve capacity is a much more important thing to consider when shopping for deep-cycle batteries.

Are There Different Kinds of Deep-Cycle Batteries?

Deep-cycle batteries come in a variety of types to suit the needs of your equipment. Each one has its pros and cons but the most important thing to remember is that you should get the best battery for your specific needs.


Flooded deep-cycle batteries are the most common type seen out in the world. They are generally the cheapest option and easy to find. However, they require routine maintenance, such as adding distilled water to the electrolyte.


AGM deep-cycle batteries have a fiberglass mat that absorbs the electrolyte in the battery. This makes the electrolyte more evenly distributed throughout the plates, which improves performance. Due to their nature, AGM batteries are also much more durable than flooded batteries and often require very little maintenance.


Gel deep-cycle batteries add a gelling agent, silica dust, to the electrolyte. This makes the electrolyte thicker and more viscous, which helps to prevent the battery from leaking electrolyte. Special chargers are required for Gel batteries.


Lithium deep-cycle batteries are the new battery taking the world by storm. They are a type of deep-cycle battery that offers several huge advantages over traditional lead-acid batteries. They are half the weight, have a considerably longer cycle life, and can be discharged more deeply without damage.

What Are Deep-Cycle Batteries Used For?

Deep-cycle batteries are more common than you might think and are used in several applications that you may use on a daily basis.

Fun Fact

The battery in your cell phone is actually a tiny deep-cycle battery. It is designed to be charged up fully, used, and then charged up again, over and over for the life of the battery.

How Long Do Deep-Cycle Batteries Last?

When we look at how long deep-cycle batteries last, we look at the number of cycles that the battery will handle. A cycle is when the battery is charged up, then used or discharged and recharged.

Most lead-acid deep-cycle batteries (flooded, AGM or Gel) will generally last around 200 cycles.

This is one area where lithium really shines. Lithium deep-cycle batteries, especially the new X2Power LiFePO4 deep-cycle batteries, are designed to last 2,000 cycles or longer.

Deep-Cycle Charging Best Practices

Keep your deep-cycle batteries healthy by following these charging best practices.

  1. Use a compatible charger: Make sure to use a charger specifically designed for the type of deep-cycle battery you have. Avoid using automotive chargers, as they may not be suitable for the different charging requirements of deep-cycle batteries.
  2. Follow manufacturer guidelines: Always refer to the manufacturer's instructions and guidelines for charging the specific deep-cycle battery you have. Different batteries may have slightly different charging requirements.
  3. Charge after use: Charge the battery after each use. Avoid leaving the battery in a discharged state for an extended period, as it can lead to sulfation and reduce battery capacity.
  4. Avoid overcharging: Deep-cycle batteries are susceptible to damage if overcharged. Modern chargers often have built-in features to prevent overcharging, but it's still essential to monitor the charging process and disconnect the charger once the battery is fully charged.
  5. Charge in a well-ventilated area: Charging lead batteries can produce potentially hazardous gasses. Charge deep-cycle batteries in a well-ventilated area to prevent the buildup of these gasses.
  6. Avoid deep discharges: Deep-cycle batteries are designed for deep discharges, frequent deep discharges can still shorten their lifespan. Try to avoid discharging the battery below 50% capacity whenever possible.
  7. Keep the battery clean: Regularly inspect and clean the battery terminals and connections.
  8. Store properly when not in use: If you plan to store the deep-cycle battery for the offseason, make sure to charge it fully before storage, and then recharge it every few months to prevent self-discharge and sulfation.

Deep-Cycle Battery Inspection

It's always a good idea to periodically inspect your batteries to avoid unsafe operation. Whenever you are handling batteries you should be wearing gloves and safety glasses to help keep yourself safe.

Check For Damage

  • Check for broken or loose terminals
  • Check the case for cracks and damage that could cause leaking
  • Check for and remove any corrosion on the terminals with a terminal cleaner

Check Electrolyte Levels

If you have a flooded battery, remove the caps to check that the fluid is covering the plates. If it's not, top off the fluid with distilled water.

Have the Battery Tested If It's Acting Up

Even if you charge and maintain your battery perfectly you should still have it tested occasionally to identify any issues that may arise so they can be corrected before it's too late.

Bring your battery to your local Batteries Plus and let our battery experts test the battery for you free of charge. If the battery is still in good shape, great! If it's time to look for a replacement, we'll help you pick out the best replacement battery for your needs. We carry deep-cycle batteries from amazing brands like Power Sonic, Duracell Ultra and our very own X2Power. Stop by today to see how we can help you!

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