Thank you Mark.
In the absence of statistics, one must sometimes go by anecdotal evidence. We have seen Bill's adverse experience with Varta, for example.
From mid-2011 to early spring 2015, our boat had 13 Deka Group 31 plain flooded truck batteries. Not even "deep cycle." Nothing fancy, held their charge very well until the last day. Never topped the water (!), except on a couple of cells out of the 18 cells that I inspected in early fall 2014... "specific gravity" was great in all 18 of them... but the prospect of periodically inspecting and re-filling 78 cells was utterly overwhelming, so I stopped after three batteries. We threw them away knowing these were perfectly healthy, well-performing batteries. I think as a budget option, Deka is a fine battery.
For the last 16 months, we've had Group 31 Trojan AGMs. No failures so far. The advantages are that these can't be maintained at all and when empty really work out the chargers –––the bulk charge phase on these is quicker as the AGMs can absorb a lot of electricity quickly, though by the time you reach about 30 amps the absorption speed curve is the same as the flooded batteries (slow).
I've gotten used to glancing at the Mastervolt Easyview on the nav table each time I go by, which must be dozens of times a day, to keep tabs on amps, volts, and temp. So far, so good, but the system has a major flaw: the temp monitoring is global, not individual to all 13 batteries. Maybe some day I'll rig a 13-battery temp monitoring station.
SM2K No. 350
At anchor, Pampelonne