Which Is Better: AGM or GEL Batteries?

It’s safe to say that battery technology has evolved significantly over the last few decades. The days of wooden encasements and glass cells are long gone, and thanks to new advancements and specialized technologies, batteries are now more efficient, powerful, compact, and environmentally-friendlier than ever.

One battery technology that has managed to stand the test of time is lead-acid. The simplicity and reliability of lead-acid batteries mean that they’re still a popular option amongst consumers looking for a cost-effective and long-lasting energy storage solution.

And despite the emergence of new battery technologies, such as saltwater and lithium batteries—and increasing competition from fuel cells—the global market for lead-acid batteries continues to grow. In fact, industry experts expect the lead-acid market to grow at a CAGR of 3.25% during the next four years and reach a net worth of over $70 billion.

When it comes to lead-acid batteries, two technologies are confused with each other more often than any other—gel and Absorbent Glass Matt (AGM). Even some of the leading battery websites have their information mixed up in terms of what each battery is and what it’s suited for. It’s true that both gel and AGM batteries are categorized as sealed lead-acid batteries, and share a multitude of similarities. However, they have distinctly different construction designs for different uses.

Over the course of this blog post, we’ll provide a detailed comparison between AGM and gel lead-acid batteries in order to help you decide which one would be best suited for your particular needs.

Both gel and AGM technologies are based on the lead-acid concept that was discovered back in 1869. In all these years, the underlying technology of lead-acid has virtually remained the same—the electrolyte is acidic, and the plates are made from lead.

When they were first introduced, lead-acid batteries revolutionized the concept of energy storage. These were the very first batteries with recharging capability. While lead was expensive, the basic design of lead-acid batteries was suitable for mass-production. This managed to keep the costs down to a level that was affordable for many applications.

Using thin plates meant that it could be used for applications that required strong, fast current surges (starter motors in cars), while a thicker plate made it ideal for deep cycle applications (refrigerators, power-lighting, etc.).

As we’ve mentioned above, the basic design that was invented over a century and a half ago is still in use today. However, it was not without its faults:

If the battery case was broken or cracked, the highly corrosive sulfuric acid could leak out.
The original lead-acid batteries couldn’t be installed at an angle, as this would increase the chance of leaking and reduce the amount of acid in contact with plates.
Since lead is a sift metal, the plates were susceptible to buckling, which causes the plate to touch and short out the entire unit or shed their active material paste.
In high temperatures, the electrolyte would evaporate, which meant that the cells had to be topped off periodically.
The first zero-maintenance sealed lead-acid batteries were introduced on a wide scale in the mid-1900s. These batteries were sealed, which stopped the electrolyte leaking or evaporating. However, these batteries didn’t resolve other issues, such as shorting out due to buckling lead plates, damage caused by leaks from a broken or cracked case, or shortened life and poor performance when installed at an angle.

Zero-Maintenance Lead-Acid Batteries
First developed in the 1970s, AGM batteries use glass fibres woven into very fine a mat which is saturated in sulfuric acid and then placed between the plates. This immediately solved a variety of issues in the older design, which is now referred to as flooded lead-acid (FLA). Since these valve-regulated batteries were leak-proof, they could be shipped without any hazardous material restrictions. The plates can be made flat to look like a standard FLA battery in a rectangular case, or they could be wound in a cylindrical cell.

The technology gained traction in the 1980s as an SLA battery for UPS and military vehicles and aircraft to improve reliability and reduce weight. Here are some of the notable advantages of AGM batteries:

If the case cracks or breaks, the acid would remain in the mat and won’t leak out.
These batteries could be mounted at any angle as the design ensured that the plate would be in full contact with the electrolyte at all times.
The mat was essentially an integral component of the batteries’ structure, holding the lead plates in place and preventing any buckling. Even if the plates did buckle, the mat would prevent them from coming into contact with each other.
The internal resistance of AGM batteries is also very low, which means they have a comparatively long service life—even when deeply cycled—and are capable of delivering high currents on demand. Moreover, AGM batteries are zero-maintenance, are considerably lighter than flooded lead-acid batteries, and provide superb electrical reliability. They can also sit longer in storage without needing a charge, as they’re less susceptible to sulfation. Furthermore, the battery has a low self-discharge and can stand up well to low temperatures.

The list of advantages doesn’t end here! AGM batteries also have a superb ability to deep cycle and a charge that is up to 5 times faster than their FLA counterparts. They perform admirably in the depth of discharge (DoD) department as well. While flooded lead-acid typically have a specified DoD of 50%, AGM batteries offer around 80%.

Because of their relatively lightweight and good vibration resistance, AGM batteries are commonly used in automobiles and airplanes. Moreover, their unique design means that the chances of acid spillage in case of a collision or an accident are relatively low. AGM batteries also offer superb cold-weather performance, which makes them suitable for marine, robotics, and motor home applications.

However, just like all other types of batteries, AGM units have their drawbacks as well. Firstly, their performance suffers in warmer temperatures. In fact, many manufacturers recommend stopping the charge if the core of the battery exceeds 49°C (120°F). AGM batteries are also sensitive to overcharging.

While AGM technology has certainly improved the flexibility in the lead-acid segment, it hasn’t eliminated all the flaws and issues. In applications with jarring or vibrations, the mat could end up rubbing against the plates, which can result in damage.

While gel battery technology was first conceived in the 1930s, it wasn’t perfected and commercialized until the 1980s. Gel batteries use an electrolyte that is similar to a silicone gel in compositions and appearance. The gel enhances the battery’s structural integrity internally and keeps the lead plates and their active material in position. The gel ‘glues’ on to the plates—essentially combining the plates and the electrolytes into one single piece, so they move in synchronization if the unit is jolted or vibrated.

Gel batteries offer a multitude of advantages that make them suitable for a wide number of applications. Firstly, just like their AGM counterparts, gel batteries don’t require any maintenance. Because of the electrolyte’s viscous, plasma-like nature, the chance of leaks is very small—even if the outer case is cracked. This means that gel batteries can be placed at any angle or position. Moreover, these batteries feature a valve which eliminates excessive pressure.

Gel batteries also have superb shock and vibration-resistance. There are no hydrogen emissions, which means you don’t have to worry about placing them in a ventilated area while they’re being charged. Also, since gel units have superior deep cycling capabilities, they also have a higher discharge feature.

Furthermore, unlike FLA batteries, gel batteries can be easily revived even after they’ve been left discharged for a prolonged period of time.

Now that we’ve discussed the advantages of gel batteries, it’s time to move on to their drawbacks—with the price being the first on the list. Compared to conventional flooded lead-acid batteries—and even AGM units—gel batteries have a considerably heavier price tag. They also have a relatively slow charge rate. Moreover, their charging needs to be halted immediately after it’s complete as it can develop voids with its electrolyte—which can potentially result in loss of charging capacity.

Another thing gel batteries need to be protected from is heat. High temperatures can have a negative impact on the saturation and composition of the electrolyte.

Because of the numerous advantages they offer, gel batteries are suitable for a wide array of applications. The most common ones include solar energy storage, ventilators in health facilities, and perhaps the most common one: electric cars.

From a theoretical point of view, the answer is simple: gel is the superior of the two technologies. However, if you look at it from a practical point of view, the price tag of gel batteries is only justified if the battery has to be good at withstanding jarring or vibration.

The use of gel batteries is quite prevalent in the industry of performance vehicles—off-roading bikes, jet skis, ATVs (All Terrain Vehicles), quad bikes, etc.—areas where jarring and heavy vibrations are commonplace. For applications like these, choosing gel batteries over AGM and FLA units is a sensible decision.

However, when it comes to most other applications, such as emergency lighting, regular automobiles, emergency lighting systems, and solar energy storage solutions, AGM batteries are the better choice due to their lower costs.

As we’ve stated in the paragraphs above, sealed lead-acid batteries (SLAs) come in two different variations—gel and AGM. However, we’ve also used a number of terms to describe both of them, including ‘zero-maintenance’, ‘sealed lead-acid’, and ‘valve-regulated’. This is probably the main reason why consumers often confuse the two technologies. Allow us to explain what these terms mean.

Although AGM and gel batteries are categorized as ‘sealed lead-acid batteries’, the fact is that they’re not truly sealed. For instance, if the unit overheats because of excessive charging, it could lead to a gas build-up which could result in the battery exploding. To prevent this from happening, both gel and AGM batteries have pressure valves that allow gases to escape once the core of the battery reaches a certain temperature.

Technically speaking, even closed FLA batteries can be termed as sealed lead-acid batteries. But with that being said, many consumers reserve the term ‘sealed lead-acid’ for gel or AGM batteries. However, don’t assume that this is universally true. Whenever you purchase a battery, always ensure you understand what the seller or manufacturer means by SLA. You can do this by verifying how the electrolyte (the battery acid) is stored within the battery:

As a liquid: this is an FLA battery which cannot be used in applications with excessive jarring or installed at an angle.
In a glass mat: this is an AGM battery and isn’t suitable for applications that involve heavy jarring or vibrations.
As a silicone gel: This is a gel battery that can virtually be used anywhere.

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