To back up Mike D's knowledge,
I found this while looking at info on a Lexus forum ( researching switching to Lexus ):

ABSORBED GLASS MAT (AGM) BATTERY INFORMATION – SS006-07 August 11, 2007
Page 2 of 3
Differences between AGM and flooded lead acid batteries:
􀀀 AGM batteries have thin, sponge–like, glass mat separators that absorb all
liquid electrolytes.
􀀀 Flooded lead acid batteries have free, liquid electrolyte all around the plates
and separators.
􀀀 Flooded lead acid batteries can easily release gas that is formed during a charge,
while AGM battery life is diminished if gas is formed during charging.
Similarities between AGM and flooded lead acid batteries:
􀀀 Both share the exact same lead acid chemistry.
􀀀 Both share the same charge and discharge principles.
􀀀 Both are safely charged by vehicle charging systems.
􀀀 When discharged, both can be recharged at high current levels.
Damage to AGM batteries becomes an issue when the charge rate is NOT monitored
and controlled by the charger (i.e., quick chargers). The performance of an AGM battery
can be irreversibly reduced if the charge rate remains too high, allowing the battery to
overheat and vent. Once an AGM battery loses water (venting), the glass mats will
become dry, causing the battery to lose conductance, power, and performance.
In most vehicle charging systems, the alternator limits the charging rate by limiting the
output voltage (about 14.4V). For example, an AGM battery may be observed charging at
60A and 13.5V. As the battery recharges, the charging voltage will increase from
13.5V to approximately 14.4V (voltage will vary based on temperature, control
sophistication, etc.), and the current will decrease from 60A to about 0A. The charging
system voltage regulators prevent both AGM and flooded lead acid batteries from being
overcharged and venting. By controlling the voltage, the charging rate (current) can
be controlled.