I wanted AGM batteries because I was killing regular batteries. Also don't mind not having any acid. I used Odyssey 975's and built boxes to make them be the same size as the originals. I got terminal covers from the marine store, even though the terminals are fairly distant from the top of the battery box. I keep them on a ctek charger.
Here's a link that I posted a while back.
http://forums.pelicanparts.com/porsche-911-technical-forum/813477-my-odyssey-battery-odyssey.html