AGM batteries - like gel batteries - are a variety of sealed cell lead acid batteries. Both gel and AGM (which stands for Absorbed Glass Mat) batteries are low-maintenance, deep-cycling, and fit for both full-time or intermittent use, like backing up a grid-tied solar system or powering a vacation cabin.
The advantage of AGM batteries over gel batteries for renewable energy storage is better performance at delivering peak power. This means you may be able to get away with a smaller battery bank if you choose AGMs over gel cells.
The disadvantage of AGM batteries over gel batteries for renewable energy storage is a shorter cycle life and somewhat higher cost per kWh cycle (however, the KiloVault 2100 PLC offers an unbeatable cost per kWh cycle).
Note: the $/kWh cycle amounts listed below are based on the battery's regular price, a 20-hour C-rate, and a 50% depth of discharge.
When they first hit the market, AGM batteries were expensive and primarily used in commercial installations where maintenance was either impossible or prohibitavely expensive. In recent years, the price of AGM batteries has fallen and they are being adopted by all types of renewable energy systems - especially grid tie solar systems with battery backup, as their self discharge rate of under 2% makes them a good option in systems that see only occasional use.
AGM batteries' sealed cells make them safe from spilling, stratification, and emitting corrosive fumes. They're extremely vibration-resistant and can be mounted on their side or end. AGM batteries do not require watering or equalization charging, and they can be transported by air.