I switched over to group 31 agm batteries about 4 years ago. (2 starting and 2 house) The pure lead batteries from Can Tire that are expensive. (over 400 each plus tax) At the time I wanted to have something that I thought was going to be reliable for many years. All the hype lead me to believe agm was the be all and end all at the time.
I only used them during the summer months on my boat and bring them into my garage over the winter and charge (top up) every couple of months. I bought 1 battery each year to make it "affordable" I just returned the first battery I purchased as it would no longer hold a charge and failed every test they put it under (load test, etc). I was lucky and caught it 2 months before the 3 year warranty expiry came into effect so I was given a replacement battery. (only 2 months warranty on it though...) The newer battery (identical) comes with a 4 year warranty now. This happening on the first purchased and oldest battery has shaken my confidence on the others. Main thing I've found is try not to run them past 50% discharge if possible. If you want to get any life out of them. I also have a few different battery monitors on the boat that I can check to see what voltage the batteries are at and what the amp draw is at any given time. Comes in pretty handy if you want to not put your batteries at risk imo. What really hurts is I had all lead acid batteries previously and got over 7 years with them with no issues. 2 of them are still in pretty good shape to this day. If I had to do it all over again, honestly I think I would stick with good quality commercial lead acid batteries. I've been reading and researching the newer LiFePO batteries and over the long run they seem like they might be a good choice. I have been using a small lithium titanate battery to run the winch on my potpuller and have been really impressed. Anyways I think the future is going to be going to these newer technology batteries soon and if you are a diy'er even building your own units from individual cells might be a good choice to look into. There are a ton of youtube video's out there on the subject.