Here's the rest of the story: After I posted that I gave up on trying to make them last... I could spend about $300-500 converting my alternator to an externally regulated unit, spend another half boat-buck on a Sterling charger, another $500 on a more sophisticated monitor and another $300 replacing my perfectly-fine MPPT solar regulator with some newer better version, then cap it all off by spending $900 on new AGMs for the house bank. OR:

I can get (Grp 24) Costco batteries for $79 each, $69 net after the $10 core value, and they guaranty them 30 months. I can buy 4 for $280 trade them in every 2 years and spend $140/year for new batteries. You can't beat $69 per battery. Screw AGM -- it will never pay for itself when Costco Kirkland brand wet cells are the "gold standard". Like changing the oil, just chalk it up to "maintenance". (written with tongue in cheek).