Monday, September 26, 2022

How To Recharge A Deep-Cycle Battery

Do you need a guide on how to recharge a deep-cycle battery? Then, read through this article for all the details you require.

This article contains information on the deep-cycle battery and the step-by-step procedures you need to follow to recharge it.

For clarity, this article is presented in sections, beginning with an overview of batteries. Then I will give a detailed explanation of deep-cycle batteries.

Next, I will show you how deep-cycle batteries work. Furthermore, the next section will contain the types of deep-cycle batteries, stating their pros and cons.

Then, I will explain the factors you need to consider to aid in properly charging the deep-cycle battery. Thus, you will find the procedures you need to follow to charge a deep-cycle battery properly.

After which, you will get the precautions you must take while charging. In conclusion, I will provide answers to some frequently asked questions on deep-cycle batteries.

So, I recommend that you read through this article before you start charging your battery.

How To Recharge A Deep-Cycle Battery: Overview

How To Recharge A Deep-Cycle Battery- Overview

battery is an electrochemical device that converts chemical energy to electrical energy. It is a combination of electrical cells to store electrical charges.

Generally, these electrical cells exist as either primary cells or secondary cells. The primary cells are non-rechargeable, so you can only use the energy in them once.

On the other hand, the secondary cells are rechargeable. Thus, you can recharge the battery when it runs low.

Hence, they are frequently called rechargeable batteries.

However, the deep cycle battery is rechargeable with a high Depth of Discharge (DoD). Thus, it releases a high amount of electricity compared to its storage capacity.

Furthermore, the deep cycle battery has fast rechargeability and can provide a steady stream of power over a long duration. Therefore, you can use a deep-cycle battery in a solar power system.

In addition, it has a reasonable discharge rate, high capacity, and high round-trip efficiency, and it recharges quickly. Its applications include marine applications, golf carts, and recreational vehicles (RVs).

More so, deep-cycle batteries apply to appliances that require enough electrical power to operate. These appliances include RV air conditioners, refrigerators, microwave ovens, and induction cooktops.

For clarity’s sake, the deep cycle battery is not the same as a starter battery. The starter battery releases short bursts of electrical power that start engines.

Thus, the starter battery does not sustain deep discharge and recharge. Instead, it only provides the starting current, after which another source runs the system.

On the other hand, the deep-cycle battery consists of thicker plates and denser active material that can withstand repeated charge and discharge cycles.

How To Recharge A Deep-Cycle Battery: How It Works

How To Recharge A Deep-Cycle Battery- How It Works

Just like every other battery, the deep-cycle battery consists of cells. Whether it is primary or secondary, the cell has two electrodes (anode and cathode).

These electrodes are partially immersed in an acidic liquid called an electrolyte. The anode reacts with the electrolyte to produce electrons, while the cathode reacts with the electrolyte to accept electrons.

Thus, a redox reaction occurs in the electrolyte. Redox simply means reduction-oxidation reaction, with the reduction reaction occurring at the cathode and the oxidation at the anode.

To prevent the electrons from moving to the cathode through the liquid electrolyte, there is a semi-permeable barrier that stops their movement. Thus, they can flow to the cathode only through the external circuit or load.

This occurs when discharging the battery. When recharging, the electrons flow in the reverse direction, which causes the chemical reaction to appear reversed.

Types Of A Deep-Cycle Battery

Types Of A Deep-Cycle Battery

A deep cycle battery can either be lithium or lead acid. However, the lead acid is further divided into a flooded lead acid battery and a sealed lead acid battery.

Also, there are two categories of sealed lead batteries. These are gel cell batteries and absorbent glass mat (AGM) batteries.

Flooded Lead Acid Battery

The flooded lead-acid battery is a wet cell that has two lead plates or grids in a container. This container is filled with liquid sulfuric acid (tetraoxosulphate iv, H2SO4) as the electrolyte.

During charging and discharging, the chemical reaction produces gases that reduce the electrolyte level. Thus, it would help if you always topped it from time to time.

However, it has a usable capacity of about 30 to 50%. The usable capacity defines how much of the battery you can use before you charge it.

More so, charging a flooded lead acid battery occurs in stages. This might lead to undercharging or overcharging.

Mostly, the charging efficiency of the flooded lead acid battery is about 70 to 80 percent.

Pros And Cons Of Flooded Lead Acid Battery


  • It is the cheapest type of deep cycle battery.
  • Also, it is reliable.
  • More so, it has a low internal impedance.
  • Even so, it can deliver high currents.
  • In addition, it has tolerance for abuse and overcharging.
  • Its shelf life is indefinite if you store it without electrolytes.
  • You can leave it on trickle or float charge for a prolonged duration.


  • They are very bulky and heavy.
  • Also, its usable capacity and charge efficiency are low.
  • Their self-discharge is as high as 5% per month.
  • Even so, it does not charge fast.
  • It is prone to overheat and generates poisonous gases during charging.
  • More so, you need to top up the electrolyte regularly.
  • The electrolyte easily spills.
  • In addition, its cycle life is low (about 300 to 500 cycles).

Absorbent Glass Mat (AGM)

The absorbent glass mat (AGM) is a valve-regulated lead acid battery with thin fiberglass mats between the lead plates. This glass mat prevents the electrolyte from moving and spilling by absorbing it.

The glass mat also serves as a damper between the lead plates. This damping action prevents the battery from shock and vibration.

Hence, the AGM battery can withstand very low temperatures. Also, it has low internal resistance and can charge faster than flooded lead-acid batteries.

The AGM battery has a charge efficiency and depth of discharge (DoD) of about 95% and 80%, respectively.

Pros And Cons Of Absorbent Glass Mat Battery


  • Its usable capacity is about 60 to 80 percent.
  • Also, it has a low self-discharge of about 1 to 3% per month.
  • More so, it has a charge efficiency of about 95%.
  • It has a higher charge rate.
  • Even so, it requires low maintenance.
  • Due to the saturated glass mats, the electrolyte does not spill.
  • Freezing temperature does not affect them.


  • It is costly.
  • Also, you can damage it by overheating.

Gel Cell Battery

This is another type of valve-regulated lead acid battery. However, the gel cell battery uses a gelled electrolyte from sulfuric acid and is suspended by water in a silica agent.

However, the charge efficiency of the gel battery is about 85 to 90 percent. In addition, it releases no off-gases and has a good heat tolerance.

Even so, it is highly sensitive to overheating. Hence, it can be irreparably damaged if overheating occurs.

In addition, the gel cell battery cannot tolerate fast charging. Thus, it requires a special charger and regulator.

Pros And Cons Of Gel Cell Battery


  • It requires low maintenance.
  • Also, it has a low self-discharge of about 1 to 3%.
  • Even so, it has a high charge efficiency of about 85 to 90 percent.
  • It has a greater level of tolerance to heat than AGM.
  • In addition, its electrolyte does not spill.
  • They are sealed.


  • It is more expansive than flooded batteries and some absorbent glass mat batteries.
  • Even so, it cannot tolerate fast charging.
  • You can damage it by overheating.
  • It requires a special charger and regulator.

Lithium Ion Battery

The lithium battery is the most recent of all other deep-cycle batteries. They are lighter than flooded lead acid batteries, with a usable capacity of about 80 percent to 100 percent.

They have an extremely long cycle life of about 2000 to 5000 cycles. Also, lithium batteries have a recharge rate that is considered the fastest.

Despite the rate of discharge, the lithium-ion battery offers a constant voltage. Thus, your lithium-ion powered lights will not dim even when the battery loses charge.

Hence, the bulb just goes out when there is no more power in the battery. However, lithium iron phosphate (LiFePO4) batteries are the most frequently used lithium batteries as banks for solar energy.

Pros And Cons Of Lithium Ion Battery


  • They are very light ad compact.
  • Also, they have a usable capacity of about 80 percent to 100 percent.
  • Even so, its rate of self-discharge is very low.
  • Its charge efficiency is about 99 percent.
  • In addition, it has a rapid charge rate, about 5 times faster than an absorbent glass mat (AGM) battery.
  • It has a life cycle of about 2000 to 5000 cycles.
  • Furthermore, its energy density is high.
  • It has a possible charge rate.
  • However, it requires no maintenance.
  • It experiences very little power loss at low temperatures.


  • It is very expensive.
  • You cannot charge them at low temperatures.
  • Also, it requires a protective system.

Factors To Consider Before Recharging A Deep-Cycle Battery

Factors To Consider Before Recharging A Deep-Cycle Battery

Before charging a deep-cycle battery, these are the factors you should consider.

Type Of Battery

The types of deep-cycle batteries are listed above. In addition, some of these deep-cycle batteries have water within them.

Therefore, before starting a charging session, you need to check the liquid levels, check for cracks on the outside, and ensure there is no corrosion on the contacts.

However, rectify any fault you find either by repairs or replacement.

Selection Of Charger

The voltage rating and current rating of deep-cycle batteries differ. Mostly, the voltage rating of the deep-cycle battery is 12 volts.

Other voltage ratings of the deep-cycle batteries include 6 volts, 24 volts, 36 volts, etc. To charge properly, you need to select a charger with the same voltage rating as the battery.

Also, these batteries have a rating of current that flows through per hour. So, for example, you will have ratings like 100A/H, 120A/H, etc.

What you need to do is to divide the ampere per hour rating by 10 to determine the current rating of the charger you need to charge your battery. The chargers commonly have output current ratings of 5 amps, 10 amps, and 15 amps.

In addition, try to inspect the wires and connectors of the charger. Thus, do not use frayed wires.

Nevertheless, you need to use dedicated lithium battery chargers or a smart AGM battery charger that has a lithium charging mode to charge a lithium battery.

Provide A Monitoring Device

In most deep-cycle batteries like AGM, the battery’s voltage reduces as the battery discharges. Also, when you are charging, the voltage increases.

However, you are expected not to allow your battery to discharge below 20% before you recharge it. This monitoring device could be a voltmeter or any device that can measure the battery’s voltage.

Now that you know the factors to consider before recharging deep cycle batteries, also there are some precautions to be taken before, during, and after charging these batteries.

Let us discuss the precautions.

Safety Precautions In Recharging A Deep-Cycle Battery

Safety Precautions In Recharging A Deep-Cycle Battery

While testing or recharging a deep-cycle battery, you must take the following precautions.

  • Wear rubber gloves and goggles while opening the battery with liquid electrolyte in case of spills.
  • Ensure the battery terminals are dry before connecting the battery charger clamps.
  • Also, ensure the charger has correct ratings that could charge your battery.
  • Always monitor your charge levels.
  • Do not allow your battery to drop below 20 percent.
  • Make sure the battery terminals and covers are free from dust and corrosion.

Now that you have the necessary precautions, let us discuss the procedures step by step on how to recharge a deep-cycle battery.

Procedures On How To Recharge A Deep-Cycle Battery

Procedures On How To Recharge A Deep-Cycle Battery

Here, I will discuss the step-by-step procedures you must follow to recharge your battery correctly. After considering the above factors, you need to follow the steps below.

However, I will state the procedures according to the type of deep-cycle battery.

For Flooded Lead Acid Deep-Cycle Batteries

In this section of this article on how to recharge a deep cycle battery, I will explain the step by step procedures for Flooded Lead Acid Deep Cycle batteries

Step 1

Ensure that all the tools and equipment you need to charge the battery are ready. Also, you put the factors above into consideration.

Step 2

Then, you must disconnect the deep cycle battery and move it to a dry and clean place with enough ventilation. For stored batteries, they are mostly not connected to anything.

Step 3

At this point, you carry out some necessary testing on the battery. For example, you need to check the battery’s electrolyte level.

To check the level of electrolyte in the battery, you use a flat-head screwdriver to remove the covers of the battery cells. You can also do this for a sealed deep-cycle battery.

This cover could be individual cell plugs or a large cap covering the cells. Use the screwdriver to pry up on the cap to remove it.

Ensure you are wearing rubber gloves and protective eyeglasses in case of splashes.

Step 4

At this point, you need to check the electrolyte. Again, you can use a hydrometer to check this by inserting the tip of the hydrometer into a cell and drawing fluid into it.

Then, you read the hydrometer based on the instructions the manufacturer provides with it. Some hydrometer use floating balls as indicators, while others use needle gauges.

However, if your test results show a low water level, you need to add distilled water. Then, you recap the cells when you are done with the test.

Step 5

After doing these things, you set your battery charger to a trickle or slow charge. Thus, you select the voltage of the deep cycle battery (6 volts, 12 volts, or 24volts) you are charging.

The deep-cycle batteries charge best with the least charge flow. Hence, set your battery charger to 20% of the ampere per hour rating of the battery you are charging – if the charger has the option to set the voltage for the charge.

Step 6

You now have to connect the cables from the charger to the terminals of your battery. Ensure that you connect the positive cable first before the negative cable.

The red-colored wire, cover, or the plus (+) sign indicates the positive terminal or wire. Also, the black-colored wire or cover or the minus (-) sign indicates the negative terminal.

Step 7

After making the connections and checking that everything is done properly, turn the charger on. To get an accurate reading of the actual charge, wait for 20 minutes and then check the meter on your battery charger.

Ensure to check the meter from time to time on an hourly basis if your charge does not have a regulator. Hence, when the battery is fully charged, you disconnect the charger.

However, if your charger has a regulator, you can leave the battery, as the regulator will automatically shut down the charger when the battery reaches the correct voltage. Thus, you can come back to check the battery at your convenience.

For Gel Cell Deep-Cycle Batteries

In this article on how to recharge a deep cycle battery, the gel-cell deep-cycle batteries do not have a liquid electrolyte. Instead, it has a gel electrolyte due to the addition of silica.

Also, they are suspended within the battery. Hence, gel batteries are spill-proof and have greater corrosion resistance.

Thus, you can not test a gel battery with a hydrometer. Instead, using a digital voltmeter is the quickest and simplest way to test the gel battery.

However, follow these steps to test and recharge the get battery.

Step 1

The first thing to do is to remove the terminal covers and disconnect the battery. Always remove the negative terminal first before the positive terminal.

Step 2

Place the battery in a clean, dry, and ventilated area and attach the clamps/leads of the voltmeter to the gel-cell battery.

Ensure that you connect the negative lead of the tester to the battery’s negative terminal. Also, connect the positive lead/clamp to the positive terminal.

Step 3

At this stage, turn on the voltmeter to determine the battery level. For example, if the voltmeter displays a charge between 12.85 volts and 12.95 volts, your battery is 100% charged.

However, if the display on the voltmeter is 12.65 volts, the battery is 75% charged. Thus, when it is 12.35 volts, it is 50% charged.

If the reading shows 12 volts or below, you need to charge the battery immediately.

Step 4

Make sure you use a float (voltage-limited charger) to charge the gel battery. A traditional charger might overcharge and damage the battery.

Always connect the charger’s positive clamp to the battery’s positive terminal before the negative terminal.

Step 5

After charging the gel battery, allow it to sit for 24 hours to allow the surface charge to dissipate and provide a more accurate reading. Then, test the battery again after 24 hours with the voltmeter.

If the charge is still low, replace the battery.

For AGM And Lithium-ion Batteries

In this section of this article on how to recharge a deep cycle battery, I will explain the step by step procedures for charging the AGM and Lithium-ion batteries

Step 1

After considering the necessary factors stated above, make sure you keep all the materials you need for the charging process ready and close to you.

Step 2

After this, disconnect the battery and move it to a clean, dry, and well-ventilated area. Ensure the temperature is suitable for the battery, between 0oC and 45oC (32oF and 113oF).

You should not charge these batteries at freezing temperatures.

Step 3

At this point, select the voltage of the deep cycle battery (6 volts, 12 volts, or 24volts) you are charging.

The AGM deep-cycle batteries charge best with the least charge flow (about 0.1C to 0.3C). On the other hand, lithium-ion batteries encourage fast charging of about 1C.

Step 4

Use the voltmeter to determine the battery level if it is necessary.

Step 5

Now, connect the clamps of your charger to the battery. Always connect the positive clamp to the positive terminal of the battery first.

Then, you connect the negative terminal of the battery with the negative clamp of the charger. Thus, put on the charger.

Step 6

Monitor the charging process either with the regulator in the charger (if the charger has a regulator), or you check the charging process hourly until the battery is fully charged.

Frequently Asked Questions

Frequently Asked Questions
1. Does A Deep Cycle Battery Need A Special Charger?

Unfortunately, you might not get the best possible results when you use the traditional charger to recharge the deep-cycle charger. This is due to the excess heat it produces.

2. Can A Completely Dead Deep-Cycle Battery Be Recharged?

Yes. It is possible to recharge a dead deep-cycle battery. According to experts, it can last for 30 days without being charged, depending on the size, type, and battery usage.

3. How Long Should I Charge A Deep Cycle Battery?

It depends on the rating of the charger. For instance, a charger with a 15 amps rating will charge a battery at 25% discharge value to full within 2 hours.

4. How Do You Revive A Deep-Cycle Battery?

You can only revive a deep-cycle battery with a liquid electrolyte. Just fill each cell with distilled water and baking soda solution, replace the caps and shake it for about 30 seconds.
However, you can’t do this with a gel battery.

5. How Many Times Can A Deep-Cycle Battery Be Recharged?

Deep-cycle batteries have 200 to 3000 discharge/charge cycles.

6. Is It Better To Charge A Battery At 2 Amps Or 10 Amps?

A slow charge is the best for your battery. However, 10 amps or less is considered a slow charge.

7. Can I Charge My Deep-Cycle Battery With My Car?

Yes. You can charge any battery with the car alternator except for built-in batteries.

8. Why Won’t My Deep-Cycle Battery Take To Charge?

Typically, it is a symptom of damage from under/overcharging, battery age, or sulfation.

9. What Should A 12-Volt Deep-Cycle Battery Read When Fully Charged?

A fully charged deep-cycle battery will read 12.7 volts and above. Some might read 13 volts.

10. What Ruins A Deep-Cycle Battery?

Charging the battery above 100%.

My Final Thoughts On How to Recharge Deep Cycle Battries

My Final Thoughts On How to Recharge Deep Cycle Battries

You might have been worried on what is the issue with your deep cycle battery. Most people might even think of buying another set of batteries simply because the initial ones have a low charge.

You also might be thinking recharging a deep-cycle battery is not that simple.

Nevertheless, if you can follow the steps pointed out in this article will help you easily recharge your batteries.

In my opinion, I will advise you stick strictly to the steps in this article.

In any case, I hope you found my PowerVersity guide to be helpful.

Please think about using the “Leave a Reply” box towards the bottom of this page to leave a remark if you found it helpful.

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Christian Jerome
Christian Jerome
Akan Christian writes for He holds an HND in Electrical/Electronic Engineering. Christian enjoys reading, listening to solemn music, singing, and playing sports. For, Christian writes reviews, buying guides, and best-pick articles.


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