Below is some possibly helpful information. It's from another forum I visit. It's taken from a discussion on AGM's:
"After much research into the AGM advantages and the primary battery manufacturers, like DEKA, Johnson Controls, Exide, etc. here are some salient points":
1. AGMs have a (lower impedance) higher power delivery rate which makes them ideal for the new start stop engines.
2. Since they are sealed they effectively recycle the hydrogen gases and recombine with oxygen to replenish the electrolyte (they don't lose water as vapor). Only when overcharged do they release gases via a high pressure valve for safety, but this does result in the battery's ultimate demise because the electrolyte balance is unrecoverably "off"
3. AGMs have a lower static discharge rate, so they are preferred for garage queens. They can be sustained, conveniently, with the same battery tenders as Flooded Lead Acid batteries, but check with the manufacturer. I know that the Griot's maintainer, Battery Tender and BMW branded tenders work A-OK, as they never exceed 14.7 volts peak charge. AGMs don't like 14.8 volts or above
4. AGMs don't mind vibration and are leak proof. A nice consideration for our trunk mounted Bimmer batteries... Motorcycle guys love them.
5. More CCA in equivalent sizes compared to LA, but not by a huge margin.
6. Since DEKA makes the AGM Super Start O'Reilly and NAPA AGM Exact Fits, they are a bargain against the OEM (BMW) AGMs. All appear to be made by DEKA....