Starting batteries don't make good deep cycle batteries, but the reverse isn't necessarily true. The AGM I installed has 50% more "cold cranking amps" than the stock battery and they wouldn't rate it that way if it wasn't intended to see duty as a starting battery, nor would they be offering a three year free replacement. As a general rule, AGM's handle higher recharge currents much better than flooded batteries do
I have a 1994 Miata which came with an AGM battery mounted in the trunk - AGM's are the stock battery in many more cars these days. Anyway, I replaced the OEM battery in my Miata with a deep cycle Optima Yellow top and that lasted me almost exactly 10 years before I had to replace it . . . . with another deep cycle Optima
When the AGM I put in my TC fails, I'll report back here . . . . if this forum is still around then ;-)
Don