Thanks so much for that research.. And so quickly. I am going to try a pair of the group 27 batteries as my house batteries in my motor home. Don't think anyone can beat that deal around here..
If you have the height available in your battery compartment, and they offer them, you would likely be better off with two 6v golf cart batteries (GC-2) wired in series for 12v.
I have lots of experience, mostly bad, cycling flooded marine group 27's.
They always required ridiculous times, held at high voltages, for specific gravity to even approach what would be considered fully charged. Even with concerted effort to get good longevity from them, it proved a lot of effort and frustratingly useless, even if it was a good learning experience.
This is not just a battery brand/ manufacturer thing, but a BCI case size thing. I tried many different brands of 27's over the years and all performed similarly. They just can't handle regular deep cycling no matter who placed the sticker on them proudly claiming 'deep cycle'
It appears to be Lead to electrolyte ratio thing that seems to get even worse with the group 29/31 flooded marine batteries. This BCI battery size was intended as a high CCA starting battery, and it just does not convert well to a good marine or Deep cycle battery, and especially if one is not overly vigilant about returning them to a true full charge in a prompt manner when cycling them to below 80% state of charge and treating them right from cycle number one, not just starting hat attempt once they are noticeably compromised to the end user.
The golf cart 6v batteries are a true deep cycle battery, the marine batteries are just slightly modified starting batteries.
Where the 27's would outperform the 6v gc-2s, would be if powering large loads on the inverter. The 12's will be able to maintain higher voltage for longer
But if high inverter or other DC load are not anticipated, and if treated equally, the 6's will likely triple the accumulated cycles of the 27's.
The GC-2s in sams and Costco are usually a bit cheaper than the 27's, Don't know about Menards.
Light Cycle vs. Deeper Cycle NOTE: This article deals with FLOODED marine batteries, not AGM or GEL batteries. The Problem: The problem, as I see it, is one of dishonest marketing where multiple battery types wear the same clothes (sticker) and will perform differently when
marinehowto.com
As always the lead acid battery lifespan is determined by average state of charge and average temperature, and deep discharges are a kick to the groin.
The best lead acid battery chronically undercharged will not last as long as the worst, kept at high states of charge.
Defects aside, if properly treated no battery should require using the warranty.
Batteries are effectively murdered by heat, and living in a chronic state of undercharge. The latter is endemic as it takes so long (3.5 hours minimum) to get from 80% to 100% state of charge, and that assumes a healthy battery held in the mid 14 volt range for that 3.5 hours, which few charger do.
That said if you often have hook ups when 'camping', then one could get away with the cheapest parallel 24s they can find.