AGM verus Gel battery: Learn the differences

Learn the differences: AGM versus Gel battery

Carmakers are switching to Absorbed Glass Mat (AGM) battery types in late-model cars and trucks to support start/stop systems. Many people don’t understand the difference between a standard lead acid battery and an AGM battery. Plus, many people refer to spiral wound AGM batteries as Gel batteries. Spiral wound batteries are not Gel batteries, they’re AGM.

What is an AGM battery?

AGM (Absorbent Glass Mat) batteries are a modern type of lead-acid battery where the electrolyte is held in place by a fiberglass mat separator. This design utilizes capillary action to distribute the electrolyte evenly throughout the battery.

The thin separator allows for high power output from a relatively compact battery size. AGM batteries are recombinant, meaning they can recycle the oxygen and hydrogen produced during charging. This process involves the transfer of oxygen gas to the negative plates, where it recombines with hydrogen to form water. This recombination is highly efficient, typically over 99%, resulting in minimal water loss.

The sealed nature of AGM batteries makes them safer and more durable than traditional wet-cell batteries. Due to the absence of free-flowing liquid electrolytes, they are also known as “dry cell” batteries. This design makes them ideal for applications requiring frequent movement or operation in various orientations.

Notice the absorbent fiberglass mats between plates and separators.

The advantages of an AGM battery

• Longer life— The lifespan of AGM batteries ranges from 4 to 8 years.

• They’re more vibration resistant— The thick cell separators and tight packing result in a battery that resists vibration.

• More capacity—AGM batteries can start a car engine over 60,000 times, about three times more than traditional batteries.

• They’re easier to charge— AGM batteries have extremely low internal resistance, charging up to 5 times faster than a standard battery. Plus, they hold their charge longer. They also generate less heat during charging, which extends their lifespan.

• They’re spill-proof so that they can be installed in non-upright positions.

• Performs better in cold weather when most flooded batteries slow down.

Now for the downsides of an AGM battery

• Easily damaged— AGM batteries can be easily and permanently damaged if overcharged or charged with a traditional battery charger. You MUST use a charger specifically built to charge these types of batteries.

• They’re more sensitive to heat— Sitting in extremely high underhood engine temps is what does them in. AGM batteries are even more sensitive to heat than flooded batteries.  That’s why more car makers are installing these batteries in locations away from the engine compartment.

• They cost more— They’re much more expensive than traditional flooded lead-acid batteries. In late 2023, a group of 35 lead-acid batteries sold for $184 at Batteries Plus stores. The same battery size in an AGM runs $259.

An Optima battery is not a gel cell. It is an absorbed glass mat battery (AGM). It uses a liquid electrolyte, not gel

While many people refer to the Optima battery as a Gel battery, it’s not. It’s a spiral-wound AGM battery. Gel batteries aren’t used as starting batteries in cars because they don’t have nearly the same starting current capacity. Instead, they’re used in uninterruptible power supplies and electronic devices.

A gell cell battery would never work well as a starting battery in a car

What is a Gel battery?

A Gel battery uses lead plates like a flooded battery, but the electrolyte is modified with silicon to transform the electrolyte into a gel-like substance.

AGM versus Gel battery — 8 big differences

1) AGM batteries can be discharged at a higher rate than gel batteries, making them a better choice for automotive starting, lighting, and ignition applications (SLI).
2) AGM batteries are typically less expensive than gel batteries.
3) AGM batteries can be used in wider temperatures than gel batteries.
4) AGM batteries have a shorter life span than a comparable Gel battery. That’s why you’ll find Gel batteries in standby power systems and UPS systems.
5) Gel batteries are less prone to leakage because they’re sealed better
6) Gel batteries cost more than AGM batteries
7) Gel batteries are heavier than AGM batteries, making them a poor choice for automotive use.
8) Gel batteries are more easily damaged at extreme temperatures.

©, 2014 Rick Muscoplat