AGM technology gained popularity in the early 1980s as a sealed lead-acid battery for military aircraft, vehicles, and UPS to decrease weight and enhance reliability. The sulfuric acid is absorbed by an extremely fine fiberglass mat, making the battery spill-proof. This enables shipment without restrictions related to hazardous materials. The plates can be made flat to resemble a standard flooded lead-acid pack in a rectangular case; they can also be wound into a cylindrical cell.
AGM has an extremely low internal resistance, is capable of delivering high currents upon demand and provides a relatively long service life, even when deep-cycled. AGM is maintenance-free, offers good electrical reliability and is lighter than the flooded lead-acid type. While regular lead-acid batteries require a topping charge every six months to prevent the accumulation of sulfation, AGM batteries are less susceptible to sulfation and can remain in storage for a longer time before a charge becomes necessary. The battery performs well under low temperatures and has a low self-discharge rate.
The main advantages of AGM Start-Stop Battery are a charging speed that is up to five times faster than the flooded version, and the ability to undergo deep cycling. AGM Start-Stop Battery offers a depth-of-discharge of 80 percent; on the contrary, the flooded version is specified at 50 percent DoD to achieve the same cycle life. The disadvantages are slightly lower specific energy and higher manufacturing costs compared to the flooded version, but it is cheaper than the gel battery. Table 1 compares AGM batteries to gel batteries in terms of key performance characteristics.
AGM Start-Stop Battery is the preferred battery for high-end motorcycles. Being sealed, AGM reduces acid spillage in an accident, reduces weight for the same performance and allows installation at unconventional angles. Due to its good performance in cold temperatures, AGM batteries are also employed for marine, motor home and robotic applications.
AGM Start-Stop Battery is making inroads into the start-stop function of cars. The classic flooded type is simply not robust enough and repeated cycling causes a significant capacity fade after only two years of use.
AGM and other sealed batteries, including AGM Start-Stop Battery, do not tolerate heat well and should be installed away from the engine compartment. Manufacturers recommend stopping the charge if the battery core reaches 49°C (120°F).