Looks like the 31 would do ok if it gets treated right. Too bad doing that is so awkward, but that's how it is.
Meanwhile we have zillions of RVs out there with 14.4v max converters so they never get their batteries looked after the best way possible. Even so those batteries last a few years, so the expense is not great.
Each RVer gets to pick and choose how much effort on batteries is worth it for his camping style.
Conspiracy lovers could imagine why converters only go to 14.4 instead of having a stage at 15.5 (so the evil battery industry doesn't collapse) :)