Absorbed Glass Mat (AGM) and Gel Cell batteries are both types of sealed lead-acid (SLA) batteries (also called VRLA – Valve Regulated Lead-Acid).
Unlike traditional flooded batteries, both AGM and Gel designs immobilize the electrolyte to prevent spills. In AGM batteries, the liquid acid is absorbed into fiberglass mats between the lead plates, whereas Gel batteries use a silica additive to thicken the electrolyte into a gel-like paste. This means both AGM and Gel batteries are non-spillable, maintenance-free, and can be installed in any orientation without leaking acid.
They also share other traits common to sealed batteries, such as low self-discharge, the ability to provide deep cycle service, and safe operation in minimally ventilated areas (they recombine gases internally).
Why AGM Batteries Work for Most Applications
AGM batteries have become extremely popular and are the go-to choice for most sealed battery needs. In fact, AGM batteries outsell Gel batteries by a wide margin (on the order of 100 to 1), largely because AGM models are less expensive to produce and purchase. AGM technology offers a variety of unique attributes that make these batteries suitable for a broad range of applications:
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High Power Output: AGM batteries have very low internal resistance, allowing them to deliver high bursts of current when needed. It's perfect for mobility scooters that need reliable acceleration power.
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Fast Charging: AGMs can accept charge quickly – up to about five times faster than equivalent flooded batteries, and faster than Gel cells as well. They don’t require special chargers; most standard lead-acid chargers (or vehicle alternators) will properly charge an AGM.
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Cold Temperature Performance: If you’ll be operating in cold climates or winter weather, AGM is typically the better choice. AGM batteries perform well at low temperatures, maintaining capacity better than Gel batteries in cold conditions.
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Reliable Deep Cycle Performance: While both Gel and AGM can be used in deep-cycle roles, AGMs have strong cycle life as long as they aren’t discharged too deeply on a regular basis. In practice, an average AGM might deliver on the order of ~1000 cycles at 50% depth-of-discharge. Keeping the routine discharge to around 50% or less before recharging helps maintain a long lifespan for AGM batteries.
Unless you have very specific requirements that favor a Gel battery (which we’ll cover next), an AGM battery will usually meet your needs reliably and economically.
When Gel Batteries Have an Edge
Gel batteries are a more specialized solution. They cost more and store a bit less power for the same size, but they shine in particular scenarios. Here are the key situations where a Gel battery may be the better choice:
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Very Deep Discharge Cycling: Gel-cell batteries are known to handle deep discharge and long-duration cycling especially well. Their design provides extra protection to the plates during heavy deep discharge. A gel battery can often survive more charge/discharge cycles at 80%+ depth-of-discharge compared to an AGM.
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Slow, Steady Power Draw: Gel batteries excel in low-current, slow discharge applications. They provide a very stable voltage output over long periods of draw. For example, running small devices or lighting for many hours is a task where gels do well. They are often used in niche applications like communications backup power, remote instrumentation, or medical mobility equipment that drains the battery slowly over time. In these cases, the Gel’s slightly lower peak power is not an issue, and its longevity is a plus.
Despite these advantages, Gel batteries come with important caveats that make them unsuitable for many common uses:
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Lower Peak Power: Gel cells cannot deliver the same high currents as an equivalently sized AGM battery. The internal gel limits how fast chemical reactions can occur.
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Slower Charging Requirements: Due to the same internal characteristics, Gel batteries charge more slowly than AGM. They also must be charged at a slightly lower voltage. Most Gel batteries require a charger setting around 0.2–0.3 volts lower per 12V battery than a standard AGM/flooded charge profile. Using the wrong charger (too high voltage or “AGM/Normal” setting) can overcharge and ruin a Gel battery quite quickly. Charging a Gel with an AGM charger can lead to gas bubbles forming in the gelled electrolyte, causing loss of capacity (a condition that cannot be reversed). Therefore, if you choose a Gel battery, you must ensure your charger is compatible or adjustable to a Gel setting.
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Cold Weather Performance: Gels do not perform as well in cold cranking or extreme cold environments. The thickened electrolyte can reduce the effective power output at temperatures near freezing and below.
Interchangeability and Final Considerations
Because AGM and Gel batteries are both sealed lead-acid types, they are often interchangeable to an extent, but with a few important considerations:
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In the majority of cases, you can replace a Gel battery with an AGM equivalent of the same size and voltage. For example, if your mobility scooter or solar backup system came with a Gel battery, installing an AGM replacement is usually fine (and often a cost-saving). It’s still wise to check the charging voltage: if the device’s charger was optimized for Gel (lower voltage), it will still charge an AGM, albeit a tiny bit undercharged (which is generally okay and certainly safe). Many mobility device manufacturers actually approve either Gel or AGM in their products as long as the size and specs match.
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If your equipment originally uses an AGM, swapping to a Gel battery may NOT be advisable unless you know the charger can be adjusted and the power demands are suitable. As we discussed, a Gel could be damaged by a charging system that is set for higher AGM voltages. Also, if the device draws high current, a Gel might struggle to deliver the same performance, leading to poor results or even premature failure. In short, do not replace an AGM with a Gel unless the manufacturer of the device explicitly allows it or you have made the necessary adjustments for charging and verified the load is within Gel’s capabilities.
Don’t hesitate to reach out to the device manufacturer or contact us for guidance. Being informed will help you get the most out of your battery and avoid any costly mistakes. Both AGM and Gel are proven technologies – it’s just a matter of picking the one that fits your needs. In most cases, an AGM will do the job brilliantly, but when those special conditions call for a Gel, it’s important to know why and to use it correctly.