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) |
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