Thanks for the quick replies. By "capacity" I was ultimately referring to the number of amps discharge per hours of time. In other words, before they die on me, I'm trying to figure out how long I can reasonably expect them to last. If I knew what they were I could just look up the specs. Some people say they can go multiple days but they usually have four house batteries.
I've got a lot of electrical/electronic experience from my work on corporate jets where I maintained the batteries and other systems but those were almost all ni-cads in my time.
For example, for the AGM link I supplied it's supposed to be able to supply 56 amps for 57 minutes, 25 amps for 155 minutes, etc. So if I'm pulling 20 amps I could expect one battery to last three hours or two batteries could last for close to six hours depending on the imbalance between them. Yet another reason I wish it had four house batteries but whatever. (I know someone who left their GT5 inverter switch turned on overnight by accident and the next day the batteries were dead.)
I know the auto-generator start could keep them from going dead as long as it's not needed during quiet hours. I just don't like surprises, especially bad ones.
The T-105's are 6V while I think these are 12 V but I didn't look that close. Maybe these are the 12V equivalent of a T-105 then.
Ray