Flooded VS Gel Batteries: What Are The Differences. Agm gel battery difference

The Complete Guide to AGM Batteries

You’ve heard the term AGM battery before and may even know that it stands for Absorbent Glass Mat. But, what does Absorbent Glass Mat (AGM) actually mean and how does that enhance the battery’s performance over standard lead acid batteries?

Let’s review some basics of the SLA (sealed lead acid) battery construction. All SLA batteries are comprised of lead plates (positive and negative) and electrolyte that are then arranged into “cells” and placed into a battery case. Some of these batteries are also valve-regulated, which allows for the escape of minor amounts of gas that occurs during the recombination process during charging. Although these batteries allow gases to escape, they are spill-proof batteries (sometimes called valve regulated lead acid or VRLA), and allow for safe operation in almost any position (the only limitation is they are not recommended to be used upside down). Because they are sealed, you don’t need to add electrolyte after the manufacturing process, and any gases that are generated go into a recombination cycle.


In AGM type batteries, the construction follows the same basics as standard SLA, with the addition of a fiberglass mat that is placed between each negative and positive plate to absorb the electrolyte. Since the mat acts like a sponge with the electrolyte, the battery becomes non-spillable.

The AGM battery holds the electrolyte in place and works by allowing the electrolyte to be passed through the fiberglass mat, creating maximum surface area for the electrolyte to touch the plates without it flooding the battery with too much fluid. AGM batteries contain only enough electrolyte to keep the mat wet and if the battery is broken no free liquid is available to leak out. This allows for less electrolyte in the battery while still providing the same energy as traditional SLA batteries.


When most people think of AGM batteries, they likely think of deep cycle battery applications. However, not all AGM batteries are deep cycle. While a popular choice for deep cycling, as an AGM battery has a depth of discharge (DoD) of 80% versus a standard flooded battery which has a DoD of 50%, it is also a popular choice for starter batteries. This is because it has low internal resistance and can provide high current loads quickly. AGM batteries are also being used as start-stop batteries in modern cars, this is due to flooded batteries not being robust enough to handle the repeated cycling in start-stop applications which can cause the battery to fail after only a couple of years use.

For example, at Power Sonic we offer our AGM technology in both deep cycle AGM batteries (the PDC line) and as a popular option in our PowerSport family (Super Sport, Ultra Sport AGM, and our Stop-Start AGM lines). However, AGM is also the technology we use in our general purpose (PS) and long life (PG) families of products as the Absorbent Glass Mat separator maximizes the surface area of the electrolyte improving battery performance.

Each cell in an AGM battery has 2 volts so AGM batteries are available in a variety of voltages including popular 6V and 12V models.


One of the advantages of an AGM battery is they can be charged up to five times faster than a standard flooded battery. As with all sealed lead acid batteries, AGM are sensitive to over-charging, we recommend this guide to charging sealed lead acid batteries to ensure get the most out of your AGM battery.


Yes AGM batteries are recyclable. than 98% of an AGM battery can be recycled. We in the battery industry are very proud of the fact that lead acid batteries are one of the most highly recycled products on the planet. AGM batteries are environmentally friendly and easy to recycle, they can be recycled at almost all recycling centers, along with many automotive outlets and thousands of other locations.


There are many benefits of AGM technology over its older flooded battery construction. One big benefit of the fiberglass mat is that since the mat holds the acid, the battery is less likely to sulfate. This characteristic is what allows it to reach a deeper DoD than it’s flooded equivalent.

The lower internal resistance of the AGM battery also has a lower self-discharge rate and therefore doesn’t require a topping charge as frequently as a flooded battery would in long term storage conditions. It is important to note that AGM batteries still must be charged before storing and will require maintenance charging while in long term storage but will charge faster than a flooded battery.

Some advantages that AGM has over flooded batteries (as well as faster charging) are increased cycle life and vibration resistance. This is because the combination of the tightly packed AGM battery and the mat inside act as a damper, which are characteristics that lend nicely to power sport applications. Another benefit of the mat is that the battery requires less electrolyte than flooded batteries, which decreases its weight.

However, one of the down sides to the AGM battery is its cost – at slightly higher than flooded, you will pay more for a battery that doesn’t need to be maintained in the same way a flooded battery does. In fact, cost is one of the reasons flooded batteries are still commonplace (usually seen more in motorsport applications).


Another popular alternative to flooded and AGM type batteries is the Gel battery. A Gel battery is still maintenance-free, its cells are sealed, and it uses a recombination process to prevent the escape of its gasses. What varies with a Gel battery is the electrolyte itself is a thixotropic gelled sulfuric acid.

When comparing a Gel battery to an AGM battery, you will see that the Gel battery’s rated capacity will decline much faster than an AGM battery’s as the ambient temperature get colder (below 32 degrees F). A Gel battery is also does not perform as well in high rate or starter applications as an AGM, which is why you don’t see Gel power sport batteries. On the plus side for Gel, it is more acid limited, giving it a slightly longer service life in some applications. Power Sonic offers Gel batteries in our DCG (Deep Cycle Gel) and our 2-volt OPzV Tubular Gel lines.


There are many differences between AGM and lithium batteries. When it comes to choosing the right battery for your application, you need to understand exactly what you are looking to get out of the battery. Is it a deep cycling application, a high rate discharge application or a float standby application? Does the application already have a built in charger for a specific chemistry? What is your budget? etc.

We at Power Sonic have put together a comprehensive guide to the differences between sealed lead acid batteries and LiFePO4 batteries, this should be able to help you to see whether AGM is the better choice for your application.

To summarize, depending on the application and your budget, you will find the AGM battery to be the more superior battery over flooded battery types due to its lower weight, lower maintenance, and overall enhanced performance. You will also find AGM to be a popular choice over the Gel batteries as they are much more common and usually less expensive. The battle between AGM and lithium batteries will depend on your application and what you are looking to get out of the battery.

If you have any questions about which battery is more suitable for your application, please feel free to call or email us.


Find the right battery for your application today. Many of Power Sonic’s wide range of sealed lead acid batteries utilize the latest in AGM technology.

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Flooded VS Gel Batteries: What Are The Differences?

In today’s automotive battery market, there are choices available for every application. Beyond the options of amp hours, cranking amps (CA) and cold cranking amps (CCA), there are differences in battery construction. These choices are among three main styles of battery: flooded lead acid batteries, gel lead acid batteries, and absorbent glass mat (AGM) batteries. What are the differences, and does charging play a factor in your choice?

Differences Between Flooded, Gel, and AGM Batteries

Flooded Batteries

Also known as a wet cell lead acid battery, a flooded battery contains liquid inside the case that interacts with the sandwich of lead and lead oxide plates. The liquid is a combination of deionized water and sulfuric acid, better known as simply the electrolyte. The electrolyte carries the charge through the battery.

Some flooded batteries are maintenance-free or sealed, while others are serviceable. In the event the electrolyte level diminishes in a serviceable battery, it can be topped up with distilled water to restore capabilities.

Because the electrolyte is low resistance, flooded batteries are ideal for high discharge applications followed by slow charging. For instance, flooded batteries are a great choice for engine starting applications. They don’t, however, tolerate deep cycle operation very well at all.

Gel Cell Batteries

The composition of gel batteries is very similar to a flooded battery. Alternating lead and lead oxide plates are immersed in an electrolyte. The major difference is the electrolyte: in a gel battery, silica is added to stiffen the electrolyte fluid. This means gel cell batteries are all maintenance-free.

The gelled electrolyte means gel batteries are safer to use and can be mounted in virtually any orientation (except upside down) without a danger of spillage. They are better lasting in hot weather and can tolerate very deep cycle operation. They are not the best choice for starting applications or high-amperage draw situations.

Absorbent Glass Mat Batteries

Like flooded and gel cell batteries, an electrolyte interacts with the battery plates. These plates may be flat, curved, or rolled. Between the plates is a layer of very thin glass fibers in which the electrolyte is suspended for the battery’s full lifetime. Like gel cell batteries, AGM batteries are all maintenance-free. Because both are maintenance free, they often get mistaken between the two despite their manufacturing differences.

AGM batteries are able to be mounted in nearly any position other than inverted, and are quite resistant to damage internally from vibration. Also, they hold a charge much better for intermittent use. Absorbent Glass Mat batteries are the optimal choice for deep cycle applications. Most can tolerate 300 or more cycles with a discharge rate of not more than 60 percent.

What Differences Are There in Charging Requirements?

Caring for a battery may not be as simple as you’d initially suspect. What works for one style can cause irreparable damage to another. Always follow the care instructions for your specific battery type.

Charging a Flooded Battery

Flooded or wet cell batteries work very well when large electrical draws are necessary. A flooded battery is capable of meeting the electrical needs quickly, although replacing the dispensed charge is a different matter. Recharging a flooded battery quickly generates high amounts of heat. The excessive heat will degrade the battery by causing the plates sulfate, resulting in a shorter life cycle than otherwise possible.

Proper charging for a flooded battery requires three stages: constant-current charge, topping charge and float charge. During the constant-current charge, a 1A charge brings the battery charge up to roughly 70 percent. The next step, the topping charge, continues the process up to about 98 percent of the full charge, and the current drops during this stage of the charge. The final stage, the float charge, brings the battery’s charge to full or near-full and maintains it there.

Charging a Gel Battery

A gel battery is intolerant of heat, much like a flooded battery. Instead of simply shortening the battery’s life, improper charging can cause immediate and irreversible damage inside, even for a new battery. When charging a gel battery, it’s critical to keep the charge rate low and slow. Otherwise, heat can cause burns in the electrolyte gel, rendering the battery useless.

A gel battery-compatible Smart battery charger is best for charging a gel cell battery. The constant-current charge rate is regulated to keep the battery from overheating, then the charger switches to float charge. A gel battery can be kept for extended periods of time on a float charge.

Charging an AGM Battery

Due to its design, an AGM battery can be charged at a faster rate than a flooded or gel cell battery. In fact, it can be charged up to five times faster than flooded batteries. Once the bulk charge has been completed, it’s critical that AGM batteries are switched to a float charge to finish off the full charge.

AGM batteries are intolerant of overcharging so an AGM battery-compatible Smart charger should always be employed.

Flooded vs. Sealed Lead-Acid Batteries Pros and Cons

Batteries come in many shapes and sizes. In the solar industry, two battery chemistries work well for our purposes: lead-acid and lithium.

We’ve written an in-depth comparison of lead-acid vs. lithium batteries previously on this blog, but here are the Cliff’s Notes: lithium is the premium option, with a longer lifespan and fewer maintenance requirements. Lead-acid costs much less up front, but regular check-ins are required to keep the battery bank working properly.

This article will FOCUS on the differences between the main lead-acid battery types used in the solar industry. You’ve got flooded lead-acid and sealed lead-acid batteries, and the latter group can be broken down into AGM (absorbent glass mat) and gel batteries.

Every battery type has a different purpose and use case, so let’s go over the pros and cons of each.

What is a Flooded Lead-Acid Battery?

For many years, the flooded lead-acid battery has been the standard in the solar industry. This type of battery is also used in golf carts and forklifts. They are the most cost effective and longest lasting of the lead-acid batteries.

Flooded lead-acid batteries contain an electrolyte that is free to move around in the battery encasement. When charged, the battery acid and lead plates react to store electricity.

These batteries are meant to be mounted upright so that the electrolyte does not leak out of the caps on top. (Since sealed batteries are…well, sealed, you can mount them in any orientation without fear of them leaking. Not the same for flooded batteries.)

While this is the most economic battery on the market, it will only reach its potential lifespan if they are maintained properly. The levels must be checked monthly and topped off with distilled water to ensure the longest possible lifespan.

Note: flooded lead-acid batteries release toxic hydrogen gas when charging. They need to be enclosed and vented to the outside to prevent this gas from being trapped and creating a hazardous environment.

flooded, batteries, differences, battery, difference

What are Sealed Lead-Acid Batteries (AGM or Gel) Batteries?

The sealed lead-acid batteries are very similar to the flooded version, but there is no access to the inside compartment. This means that you do not have to add distilled water. The electrolyte is sealed inside, and there is enough to allow the battery to live out a calculated number of cycles.

You sometimes see these referred to as VRLA (valve regulated lead-acid) batteries, because they have a small valve to allow for the escape of the gasses that occur during charging.

What is an AGM (Absorbent Glass Mat) Battery?

Absorbent Glass Mat batteries are the most popular VRLA battery because they can work in a wide range of conditions. The electrolyte is suspended in a thin fiberglass mat that is situated between the lead plates. This allows the battery to be resistant to vibration, which makes them a great choice for RV and other mobile applications.

They can also be mounted in any orientation. It is common to see them mounted on their sides for convenient placement and wiring.

AGM batteries are more expensive than flooded lead-acid batteries, and they do not last quite as long. But for that extra price, you get the luxury of not having to maintain the batteries or deal with as much gas that is released during the charging phase.

They are perfect for mobile applications, places where leaked acid would be problematic, remote locations where maintenance will not be possible on a regular basis, and places where the batteries could be subject to extremely cold temperatures.

What is a Gel Battery?

Gel batteries are another VRLA battery very much like an AGM, but they use a thick paste that allows the magic to happen rather than the fiberglass mat.

flooded, batteries, differences, battery, difference

The main difference between gel and AGM batteries is the charge rates. AGM batteries can handle higher charge and discharge rates than gel batteries.

Gel batteries are the most costly of the VRLA batteries, but excellent candidates for projects that need a very slow deep discharge. They also last a bit longer in hotter temperatures, so you might pick them if you are concerned about high ambient temperatures in the space where the batteries are enclosed.

Gel batteries are more expensive than other lead-acid battery types, so they are not ideal outside a handful of specific solar applications (very hot climates, mainly). The technology has been eclipsed by other battery types that have been developed more recently.

It is very common for people to mistake a Gel for an AGM, and this can affect the lifespan of the battery. Gel batteries are the most sensitive of the VRLA batteries, and It is critical that the correct charging parameters are used when you have a Gel battery in your application.

My Experience Living Off the Grid

When I first started living off the grid in 1996, I had never heard of a Gel or AGM battery. Everyone I knew that was exploring the off-grid lifestyle used the flooded golf cart batteries. Once I started working in the industry and doing more installations, I started seeing more battery options.

I quickly realized that the bigger flooded batteries called L-16s were the standard in most of our nicer installations. These are sometimes referred to as a forklift battery. While the cost per amp hour was similar to a golf cart battery, it became evident that the L-16s lasted longer. It was explained to me that the bigger the battery, the thicker the lead plates would be, therefore gaining a better lifespan.

About three years ago, my flooded batteries were at the end of their life, and I opted to get AGM batteries this time around. While I don’t really notice much performance difference, I am relieved to not have to crawl under my stairs to check water and maintain the batteries anymore. Even though my L-16s were in a sealed vented compartment, once in a while I would catch a whiff of something that must have been the hydrogen gas seeping out. I haven’t smelled that since, and it was worth every penny to make the switch.

For more advice on which battery type is best suited for your project, chat with one of our system designers or grab a copy of our Solar Battery Guide, or our guide on deep-cycle batteries that covers all you need to know about these stable battery types.

Are Gel Batteries Better For Solar?

The modern gel battery was invented in 1957. Gel batteries are one of two sealed lead acid batteries, the other being an AGM battery. Sealed lead acid batteries are distinct from other lead acid batteries in that they are maintenance-free.

What’s in a gel battery?

A gel battery is a dry battery since it doesn’t use a liquid electrolyte. In a gel battery, the electrolyte is frozen with silica gel. This keeps the electrolyte inside the battery, preventing it from evaporating or spilling.

This design stabilizes the battery and gives it a low self-discharge. This is a handy feature for batteries that lie idle for long periods.

Are gel batteries better than flooded batteries?

A flooded lead acid battery is a wet battery since it uses a liquid electrolyte. Unlike a gel battery, a flooded lead acid battery needs maintenance by topping up the water in the battery every 1-3 months.

Gel batteries are the safer lead acid batteries because they release less hydrogen gas from their vent valves. This makes them safer to install where there is limited ventilation. Hydrogen release or gassing is a minor safety concern with flooded lead acid batteries.

flooded, batteries, differences, battery, difference

Because of how they’re made, they can be oriented in any way. They can be stacked pancake-style which may improve cycle life. Flooded lead acid batteries are kept upright to avoid acid spills.

Gel batteries are, however, more expensive. Check out this guide if you’re curious about how flooded lead acid batteries work.

Are gel batteries better than AGM batteries?

Absorbent Glass Mat (AGM) batteries are the other sealed lead acid battery. How do gel batteries compare to AGM batteries?

For starters, gel batteries can be more expensive. They also need specific chargers to prevent overcharging. Not using these chargers reduces the batteries lifespan.

They’re also don’t work as well with appliances that need a higher current because they have a higher internal resistance.

On the other hand, gel batteries have a longer lifespan. This is because:

  • They hold more acid because of their design.
  • They have a better temperature tolerance. They have improved heat transfer to the outside. The gel moves heat, whereas the absorbent glass mat of the AGM acts as an insulator.
  • They also maintain their performance over a longer period. AGM batteries gradually fade as they get older.

Check out my guide to AGM batteries for more on absorbent glass mat batteries.

When should you choose a gel battery?

Gel batteries are an alternative to flooded lead acid. They’re suited for a battery backup system or an off-grid home. If you don’t mind the extra expense, a gel battery is a better option if you’re looking into lead acid batteries. This is because you won’t have to worry about maintenance.

Pros and cons of gel batteries

To summarize, here are the advantages and disadvantages of a gel battery.

Advantages of a gel battery

  • Maintenance-free.
  • 6-year lifespan.
  • Better performance until its end of life then performance drops off sharply.
  • You can install it sideways since it’s spill-proof.
  • Better heat tolerance.

Disadvantages of a gel battery

  • You need to store it in a charged condition although this is less critical than as for a flooded lead acid battery.
  • It requires some ventilation as it releases gas when pressure builds up.
  • Sensitive to overcharging though this is less so than AGM batteries.
  • AGM is cheaper and can handle higher loads.

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