Is this a deep cycle battery?

I'm not expert, but I can't imagine a 4D AGM that wasn't designed for house bank or deep cycle use. What else would you use them for?

You say drop in replacement, so presumably that is what is there now. I still don't take for granted that the prior owner properly set up for AGM charging. The shore powered battery charger needs to have an AGM setting and your alternator needs a temperature controller at the least, or it could burn out. AGMs are good batteries, but they are very finicky with charging requirements, especially when deeply discharged. AGM start batteries or light house use are very different.

The other thing that strikes me is using 4Ds. They must weigh something in the 130 lb range. I hauled four group 31 batteries around at maybe 70 lbs each and was at my limit in some very awkward angles. I think I would rather be waterboarded than hump around a 4D.

Icarus05 said:

So I called Deka and they say they are "deep cycle". I also have read Maine sails posts about Deka vs Lifeline et.al. AGMs. That being said, I think I'm going to switch to flooded for many of the reasons you and others have mentioned.

I'm looking at 2 or 3 US battery group 31s. Nothing but good things said about them and I think they would fit better with the charging system; Link 2000 R.

What is the best battery box option for these batteries? Is just a tray enough or should I have a fully enclosed box? Space is limited.

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Whatever you use, you need to insure the charging profile of your equipment is compatible. AGM, Gel, flooded are all different. I don't think swapping one type for the other is that simple. However, I'm also unsure which type the 2000r regulator is designed for. Maybe it has user settings for each. Your PO may have mismatched, killing the current AGMs.

As for the box, I would suggest a full box for flooded. They could leak, after all, unlike AGMs or Gels. More importantly, they need to immobilized, so,they don't bang around and break. Sitting inside a loose box isn't good enough, IMO. Brace them and provide a box to collect a leak.