An AGM battery is an absorbed glass mat product. It is often confused with gel cell battery products. Each type has similar aspects like being unable to be spilled, being able to be mounted in any fashion and being capable of being used in areas with limited ventilation. They are also capable of deep cycling and having low self-discharges.
The glass mat of an AGM battery is made to take the electrolytes from the battery and wet the mat just enough to keep the battery running. With gel batteries, there is a silica gel between the electrolyte that lets electrons flow in between the plates.
AGMs tend to be favored over gel cells. It is the best type to use when a high degree of amps are needed. If these batteries are not discharged more than half their full capability over time they can last for many years. Deep cycle abilities vary with the individual AGM product.
AGM batteries recharge much faster than gel batteries do. They also cost about the same as the gel formats. It should be noted that just because a product is labeled as AGM it does not necessarily mean that it is a deep cycle battery.
The manufacturer of the product will indicate if the AGM is a starting battery or if it is any other type of non-deep cycle type of battery. The product usually will have the same ability to benefit the user as most AGMs do, but they cannot function as deep cycle batteries alone. The plate thickness of the product is what dictates whether or not it is deep cycle.
Among the top makers of these batteries is Concorde. They make a line of AGMs that include the Sun Xtender, the Lifeline, and the Chairman. The Sun Xtender has a bolt on terminal rather than a post terminal. This gives the battery a better, more reliable connection.
These batteries can be used for marine applications, they can be used in RVs and they are well suited to use in wheelchairs, too. Choosing a battery should be based on how much efficiency it can offer. Look for the amount of internal resistance that the battery has. Also, note its total charge and discharge abilities and its ability to deliver high currents without dropping voltage. If you are picking out an AGM for the first time, stick to brands that have proven performance.