A relatively new type of sealed battery construction that uses saturated absorbent glass (boron silicate) mats between the plates instead of a gelled or liquid electrolyte. AGMs batteries are more expensive than the flooded (liquid) variety but offer a number of advantages.

Since all the electrolyte (acid) in AGM batteries is contained in the glass mats, it can't spill, even if the battery is broken. Being thus non-hazardous, AGM batteries are cheaper to ship. Additionally, since there's no liquid to freeze and expand, they're practically immune from freezing damage.

Nearly all AGM batteries are recombinant, which means that the oxygen and hydrogen recombine inside the battery. Recombinant batteries use gas phase transfer of oxygen to the negative plates to enable recombination back into water while charging, thereby preventing the loss of water through electrolysis. The recombining is typically more than 99% efficient.

The charging voltages are the same as for any standard battery, so there is no need for any special adjustments and no problems with incompatible chargers or charge controls. Since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents.

AGMs have a very low self-discharge - from 1% to 3% per month is usual. As a result, they can sit in storage for much longer periods without charging than standard batteries.

Even under severe overcharge conditions, hydrogen emission of AGM batteries is far below the 4% maximum specified for aircraft and enclosed spaces. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.

Even with all the advantages listed above, there's still a place for the standard flooded deep cycle battery. AGMs cost 2 to 3 times as much as flooded batteries of the same capacity. In many installations, where the batteries are set in an area where you don't have to worry about fumes or leakage, a standard or industrial deep cycle is a better economic choice.

Do you know what the wear on the plates is ? Lifetime of the battery before replacement ?

i haven't found out about the wear on the plates i believe that their is little to no wear. the typical lifespan is 3 to 4 times longer then a lead acid battery or a gel type battery i will continue to find more information on agm, gel , and lead acid battery

AGM - new??? Not in this country. They have been around for decades in all sorts of equipment. And the liquid in the mats CAN freeze.

There is a major point regarding AGM and sealed valve lead-acid {SVLA} batteries. First is that there is the possibility of damaging the battery by charging at too high a rate. This causes gas bubbles, which translates to dry spots on the plates, reducing the capacity in AGMs, or can cause outgassing in SVLA batteries.

AGM batteries were developed and put into use in the 1980's by and for Military use. Questionable, yes! Because of the no name agencies usage and not releasing for public use, real date therefore cannot be determined.
Though information seems to be manufacturer specific and green related, here's what seems to be the general consensus,

Advanced AGM Advantages

- Classified as "NON-SPILLABLE BATTERY"
- Spill proof / leak proof
- No corrosion
- Acid starved. High active material to acid ratio for long life in cyclic applications.
- Micro fibrous silicate glass mat acid absorption along with charge control eliminate water loss
- Excellent for multiple medium duration deep discharges
- Excellent for Medium Duration BACK UP POWER and RENEWABLE ENERGY applications
- Excellent for UPS/TELECOM and HIGH RATE applications
- Very good deep cycle life with good starting ability.
- Superior energy density over gel batteries
- No loss of capacity as a result of viscous degradation or voids in gelled electrolyte
- Installs upright or on side (side installation may lose 10%-15% capacity and life will be affected)
- Very low to no gassing (unless overcharged) By design 70% less than requirements even at
increased temperature and charge voltage
- Compatible with sensitive electronic equipment
- Superior shelf life
- Superior recharge ability (from 0% to 90% in 4 hours)
- Superior recharge ability (from 0% to 100% in 6 hours)
- No recharge current limitation @ 13.8~14.7 volts
- Rugged and vibration-resistant
- Very safe at sea with no chlorine gas in bilge (due to sulfuric acid and salt water mixing)
- May be recycled at any smelter that processes lead acid batteries
- Operates in wet environments...even under 30 feet of water
- Good in extreme temperature applications. Will not freeze to -20°F/-30°C (if fully charged)
- Low Life Cost per Amp Hour or Kilowatt Hour (cost/total energy supplied)
- Low cost-per-month (cost / months of life)
- Low cost-per-cycle (cost / life cycles) - Up to 40% more cycles than standard deep cycle
absorbed electrolyte batteries when discharged capacity exceeds 80%
- Up to 7 times the cycling ability of standard AGM when discharged capacity exceeds 50%
- Up to 5 times the cycling ability of standard AGM when discharged capacity exceeds 80%
- *> 400 cycles when discharged to 20% remaining capacity
- *> 800 cycles when discharged to 50% remaining capacity
- *> 2500 cycles when discharged to 80% remaining capacity
* Actual results will vary depending upon application by battery, discharge rates, charging regime and
temperature etc.

read more here,

http://www.discover-energy.com/files/sh ... 2009_1.pdf

As stated in some of the research I have done, to predict the life of any battery would involve the date of purchase and the day the battery failed, add time in between, wah laa!
A battery's life cannot be predicted, only estimated. Usage and continued draw within specs , to include maintenance and monitoring, could greatly increase the life of any battery.
Most one can expect is to monitor the increase in resistance and replace based on the acceptable readings.

Bottom line, A glass mat battery "should last 4x longer" than lessor technology.