I did a Google search on AGM batteries. These are the latest in battery technology. In a nutshell there are three types of lead acid batteries. 1. The conventional flooded plate batteries where the sulfuric acid is liquid and free to slosh around in the cell. 2. The Gell Cell where the acid is mixed with additives to turn it into a gell. The plates are then submerged in the gell much like the flooded cell. 3. AGM or Absorbed Glass Mat, these have a special fiberglass mat saturated with acid sandwiched in between each plate. The plates and mats are stacked in each cell then compressed to fit in the cell. The result is that the plates are extremely stable and supported against vibration and if the case is punctured the acid will not leak out.
AGM batteries are used in highly critical applications such as aircraft, marine and computer UPS (uninterruptable power supplies) systems just to name a few. I have been doing a fair amount of research becasue I need to replace the OEM batteries in my Duramax and I want the best I can buy. There are a couple of themes that kept poping up when I was researching. 1. Optima has a lot of people complaining about the Optima quality on a lot of forums. 2. The Odyssey AGM batteries keep being mentioned as the battery to buy. Interestingly Sears DieHard Platinum is an AGM battery which is made by Odyssey for Sears and rates as high as the Odyssey battery for about $50 less.
Here is a Wikipedia article which explains AGM batteries:
http://en.wikipedia.org/wiki/VRLA_battery
A link to Odyssey's web site:
http://www.odysseyfactory.com/index.html
Sears DieHard Platinum page:
http://www.sears.com/shc/s/p_10153_1...9&blockType=G9