Absorbed Glass Mat (AGM) batteries were originally developed for the military. They are designed and built tough, and will take an enormous pounding. They are designed to withstand shock and vibration better than any standard battery:
AGM Batteries are still lead-acid batteries but are sealed instead of vented. The electrolyte is held captive in a fibrous glass mat that can’t be spilled and therefore can be shipped without hazardous material restrictions.
AGM Batteries are totally sealed and spill proof; can be mounted in any position or direction.
Due to low internal resistance, they can be fully recharged at a lower voltage and accept a larger current (amps)
AGM batteries discharge time is much slower than conventional deep cycle batteries.
AGM batteries can be recharged up to 5 times faster than a regular wet cell battery.
Discharge rate of AGM battery is not more than 3% per month and even after 12 months sitting idle can be recharged and put back to a full charge. A normal wet cell battery discharges at a rate of up to 15% per week.