What’s the Better Deep Cycle Battery: AGM or Gel?

So, you need a new 12V deep cycle battery for your golf car, your caravan, your utility vehicle, or your fishing boat? And you’re wondering which choice is better -- an AGM battery, or one of the gel variants on the market?

It’s a common question we get here at Battery Specialists, and we’re taking some time today to answer it for you.

We’re going to begin by looking at what, exactly, these batteries are. Then, we’ll examine each type in some detail. Finally, we’ll do a side-by-side comparison so you’ll know definitively why the AGMf deep cycle battery comes out on top.

Let’s get going, shall we?

What Are Deep Cycle Batteries?

We use all sorts of batteries every day without much thought to their types, or how they differ. We usually only worry about the batteries in our lives when they quit working, right?

There’s the button cell battery in your car’s keyfob. Then there’s the AA or AAA in your TV remote. Your car battery is a cranking or starter battery, giving a sudden burst of charge to start the motor.

How do these batteries differ from deep cycle batteries? It’s simple. Their Depth of Discharge.

A battery’s depth of discharge (DoD) is how long it can be used before having to be replaced or recharged. The level of discharge is how much power can be drawn from the battery at any one time.

The battery lifespan, or how long they last, in deep cycle batteries is much longer due to their high DoD.

Car batteries have a discharge rate of 2 to 5% each time you crank the motor over. The deep cycle battery in your fishing boat, however, can discharge up to 80% of its stored energy before needing a recharge.

That starter battery also has thinner, lighter lead plates inside. Deep cycle batteries, on the other hand, consist of heavier, thicker lead plates.

And that’s what defines a deep cycle battery from all the other valve activation lead acid batteries in existence.

Deep Cycle Absorbent Glass Mat (AGM) Batteries

Every deep cycle lead acid battery is made up of lead plates and an electrolyte solution of sulfuric acid that creates the chemical reaction that produces an electrical charge. You can see how this works in the video below.

AGM batteries are made with an absorbent fiberglass mat that absorbs the sulfuric acid electrolyte solution between the lead plates inside the battery. This mat is what gives the battery its name. And several advantages over gel batteries, as we’ll see.
There was a growing demand in the 1980s for batteries that were lighter and safer than the old traditional lead acid batteries on the market.

The growing market in smaller, lighter aircraft, personal use vehicles like golf and utility cars, and mobility scooters for the aging population needed safer, lighter power sources. The deep cycle AGM battery was the answer.

Your car’s heated seats, electronically adjusted steering wheels, mirrors, and seats may also be powered by a small AGM battery.

Not only did AGM batteries meet power requirements in a less hazardous, more efficient way, the innovation of the glass mat meant that 12V deep cycle batteries could lose their rectangular shape, becoming cylinders and other “odd” shapes to fit their use.

The design of the glass mat separator also gives AGM batteries quite a bit of vibration resistance. This makes them perfect for motorbikes, quad bikes, boats, camping appliances, and other items which receive a good bit of bouncing, bumping, and vibrations.

Some other pros of using an AGM battery:

• Can last 4 to 7 years
• Cheaper — three times cheaper than lithium batteries, for example
• Quickly recharge
• Perform well in temps below 0℃ and above 80℃

There are a few disadvantages to using an AGM deep cycle battery. They are:

• Reduced charge over time — the AGM battery range (charge capacity) gets lower the longer in use 
• Sensitive to overcharging, shortening lifespan
• Low specific energy load, making them unsuitable for some applications

Deep Cycle Gel Batteries

The “gel” in a gel deep cycle battery is a special type of thick silica gel that holds the sulfuric acid. The thick consistency of the silica gel doesn’t move around much, meaning these batteries can be installed at all kinds of angles and positions without fear of leakage.

The chemistry involved in gel batteries produces little to no fumes, making them ideal for situations where there isn’t much ventilation.

The use of the silica gel, as opposed to the typical water and sulfuric acid mixture, makes gel batteries virtually maintenance free.

Now, let’s take a look at some other advantages to using a gel cell lead acid battery:

• No leaks - the gel doesn’t go anywhere
• Install anywhere, in virtually any position
• Resistance to discharge “death” as long as they are properly charged

There are serious disadvantages to using gel batteries over AGM batteries, though, and we can’t ignore them. Some of them include:

• Higher costs - AGM batteries outsell them 100 to 1
• Shorter life span - 2 to 5 years
• Operating temps of -20℃ to 45℃
• Heavier - the gel adds a lot of weight
• Lower power capacity than an AGM deep cycle battery
• Charging issues - a gel battery requires a specialized charger or you shorten the cycle life and cycling performance of the battery, whereas AGM deep cycle batteries do not
• Charging time - 5 times slower to fully recharge than an AGM battery
• Overheating - gel batteries have been known to overheat and even catch fire

Side by Side Comparison: AGM vs Gel Deep Cycle Batteries

Now, let’s put all this together in a side-by-side comparison chart. We’ll look at the areas buyers are most frequently concerned with, and we’ve ticked each concern to show the battery that comes out on top.