AGM Batteries VS Gell Batteries
AGM batteries (Absorbed Glass Mat) are a special design glass mat designed to wick the battery’s electrolyte between the battery plates. AGM batteries contain only enough acid to keep the mat wet with the electrolyte and if the battery is broken no free liquid is available to leak out. In most cases if the battery is broken, it will still work well. This will allow for enough time to replace the battery.
Gel-Cell batteries contain a silica type gel that the battery electrolyte is suspended in. This thick paste like material allows electrons to flow between plates but will not leak from the battery if the case is broken.
More often than not AGM Batteries are mistakenly identified as Gel batteries, Telkom batteries, non spillable batteries, lead crystal batteries, dry cell batteries, or even waterless batteries. This is because both batteries have similar traits; such as, non spillable, deep-cycle, may be mounted in any position, low self-discharge, safe for use in limited ventilation areas, similar weight, looks similar, and may be transported via air or ground safely without special handling or permits.
AGM Batteries outsell Gel-Cell batteries by at least a 100 to 1. AGM is preferred when a high burst of amps may be required. In most cases recharge can be accomplished by using a good quality standard battery charger or engine alternator. The life expectancy, measured in cycles or years, remains excellent in most AGM batteries if the batteries are not discharged more than 80% DOD between recharge. There are some AGM batteries that offer a 100% DOD deep-cycle abilities.
Gel-Cell Batteries on the other hand are typically a bit more expensive and do not offer the same power capacity as AGM batteries - comparing it with the same amp-hours. Gel-Cell batteries have a similar DOD to flooded batteries, which is about 50%. They also do not deliver the cycle life than AGM batteries.
Gel-Cell batteries excel in slow discharge rates and slightly higher ambient operating temperatures.

One big issue with Gel-Cell batteries that must be addressed is the GEL charge profile. Gel-Cell Batteries must be recharged correctly or the battery will suffer premature failure. The battery charger being used to recharge the battery(s) must be designed or adjustable for Gel-Cell Batteries. If you are using an alternator to recharge a true Gel-Cell battery, a special regulator must be installed. This causes a lot of Gel-Cell batteries to fail. And if under guarantee, the manufacture will not replace the battery.