Where did you get your AGM battery?
I saw some on the shelf at wally world that claimed to be AGM, but you had to add the acid to it before use. Uhh.. that's not a "sealed AGM" battery.
I have this companies AGM batteries in all the toys (two bikes and two PWC's). I bought one of theirs for my FJ 5 years ago and never had an issue. I took it out and put it in a FJ I fixed up and sold not too long ago. Still works fine, and I bought my FJ a new one.. just because I could.
http://www.dekabatteries.com/