AGM Batteries

Absorbent glass mat (AGM) is a class of lead-acid battery in which the electrolyte is absorbed into a fiberglass mat. The plates in an AGM battery may be flat like wet cell lead-acid battery, or they may be wound in a tight spiral. The internal resistance of AGM batteries is lower than traditional cells, they can handle higher temperatures, and self discharge more slowly.

These batteries have a valve which will activate when the battery is recharged at high voltage. Valve activation allows some of the active material to escape thus decreasing the overall capacity of the battery. The lids /vents typically have gas diffusers built into them that allow safe dispersal of any excess hydrogen that may be produced during charging. They are maintenance free; and they can often be oriented in any manner, unlike normal lead-acid batteries which must be kept upright to avoid acid spills and to ensure the plates are sitting in the electrolyte.

 AGM batteries are totally sealed and are easy and safe to transport

• They NEVER topping up with water

   

• They can be safely mounted inside a boat, car, caravan

   

• AGM batteries only need to be vented to atmosphere, they do not need to be in a sealed box vented to the outside like wet batteries, and can be mounted on their sides or ends if needed.

   

• Due to their very low internal resistance AGM batteries will fully charge at a lower voltage, and accept a much larger charge current, so when charging from a standard car/truck alternator these batteries will all but fully charge, and they will charge quickly, in about 3 hours!

   

• AGM batteries can be discharged deeper than conventional deep cycle batteries without major damage.

   

• AGM batteries only self discharge at the rate of up to 3% per month, and even after 12 months sitting idle can be recharged and put back into full service without any major damage. (A standard deep cycle battery if treated the same way will have destroyed itself, it will no longer hold a good charge)

   

• AGM batteries were originally developed for the military, they are very robust.

   

Battery Maintenance

 Deep cycle batteries such as those used in solar power systems have much thicker lead plates to make them last longer. Deep cycle batteries should never really be discharged to below 20% of their full capacity, because internal resistance causes heat and damage when they are recharged. Renewable energy systems usually use a low-charge or low voltage warning light or a low-voltage cut-off switch to prevent the type of damage that will shorten the battery's life.

 Battery shelf life can be extended by storing them at a lower temperatures, because the chemical reactions in the batteries are slower. However, in order to reach their maximum voltage, batteries must be returned to room temperature. Therefore, most battery manufacturers do not recommend refrigerating batteries.

 Battery safety, explosions and other hazards

 A battery explosion is caused by the misuse or malfunction of a battery, such as attempting to recharge a non-rechargeable battery or short circuiting a battery. Explosions are most likely to occur when a short circuit generates very large currents. In addition, deep cycle batteries can release hydrogen when they are overcharged (due to electrolysis of the water in the electrolyte). Normally the gas dissipates quickly. However, this gas can be ignited by a nearby spark (for example, when removing the jumper cables).

 Attempting to charge a battery beyond its electrical capacity, ie overcharging, can also lead to a battery explosion, leakage, or irreversible damage to the battery. It may also cause damage to the components in which the overcharged battery is used.

 When a battery is recharged at an excessive rate, an explosive gas mixture of hydrogen and oxygen may be produced faster than it can escape from within the walls of the battery, leading to pressure build-up and the possibility of the battery case bursting. In extreme cases, the battery acid may spray violently from the casing of the battery and cause injury.

 Battery explosions can also occur in maintenance free lead-acid batteries if the valves fail or are blocked. The pressure rises within the cells until a short-circuit ignites the hydrogen-oxygen mixture. Such explosions can cause severe injury. The problem can be detected in most batteries if the sides appear swollen, or if the battery feels hot to touch.