Translations:Fonctionnement, entretien et régénération de batteries au plomb/44/en

AGM batteries are a type of sealed/VRLA battery, in which the electrolyte is a liquid but it is held in place in a fiberglass blotter, and hence its name: Absorbed Glass Material.
View the inside of an AGM battery

Advantages Disadvantages
Maintenance-free with minimal release of gas They do not perform well in hot conditions (loss of electrolyte in the form of gas at higher temperatures) A temperature above 49°C (120°F) is very dangerous for the battery life.
They maintain the electrolyte homogeneity well. They are sensitive to overcharging and high voltages (loss of electrolyte in the form of gas)
Withstand colder temperatures well because of their homogeneous electrolyte (Since the electrolyte is held in the glass mat separators, it won't expand when frozen like it will in a flooded battery) They have limited shelf-life. (as the acid concentration inside is higher than in others, which leads to faster battery degradation). )
Allows high peak currents (CCA) to pass
Shock-resistant (Vibration-resistant) (Because of the fibre glass mats are woven tightly and the plates are packed tightly, making them immune to vibrations)
Low self-discharge (1-3% per month)