AGM 's are typically VRLA, valve-regulated lead-acid
and are a type of low-maintenance lead-acid
rechargeable battery. Because of their construction,
VRLA batteries do not require regular addition of water
to the cells. VRLA batteries are commonly further classified
• Absorbent glass mat battery
• Gel battery
Instead of using a gel, an AGM uses a fiberglass like
separator to hold the electrolyte in place. These types
of batteries have all the advantages of gel cell batteries,
but can take much more abuse. They are also called "starved
electrolyte", as the mat is about 95% saturated
rather than fully soaked. That means that they will
not leak acid even if broken.
Some advantages over gel cells and flooded deep
• they cannot spill, even if broken, as all electrolyte
(acid) is contained in the glass mats. In addition,
since there is no liquid to freeze and expand, they
are practically immune from freezing damage.
• charging voltages are the same as for any standard
battery - no need for any special adjustments or problems
with incompatible chargers or charge controls.
• low self-discharge - from 1% to 3% per month
is usual. This means that they can sit in storage for
much longer periods without charging than standard batteries.
Basically, an AGM can do anything a gel cell can, only
better. However, since they are also sealed, charging
has to be controlled carefully or they can be ruined.