sealed Flooded Lead acid

[Bala]

The "maintenance free" batteries that i am familiar with are all automotive starting batteries. They are still vented, just with non-obvious vents. And in every case I have seen you can, with the right tools, non-destructively pry open the vent caps to either use a hydrometer or add water to the cells. Not as easily as with conventional caps (and I really hate the conventional caps that cover three cells with a single piece vent cover!) but well enough to do a cell-by-cell SG check or add water if it turns out that the battery needs equalization.
That said, I am not really comfortable in the first place with any CC that automatically tries to perform true equalization rather than just an extended absorb.

I tried getting the tops of one a little while ago, definitely destructive getting it off, there are some now where the tops are well and truly glued on.

[PNjunction]

In Europe and elsewhere, leisure-batteries are marketed as deep-cycle as they are not really intended to start the car. A quick generic consumer type guide for them can be found here:

http://www.campingandcaravanningclub.co.uk/helpandadvice/technicalhelp/datasheets/guide-leisure-batteries/

Sure enough you can open the caps on the flooded/sealed ones and replace electrolyte, but for most leisure type caravan duties, the owner isn't really interested in hydrometers. With cooler temps and as long as one doesn't try to EQ it, the premise is that you can leisurely ignore maintenance for a few years.

Compared to a TRUE deep cycle, the leisure types are what would be a "cheep and cheerful" solution for the odd outing. They make ok "learner batteries", but those with serious daily-cyclic or more advanced setups will want a true deep cycle. Similar, but not exactly the same as to what we do on this side of the pond graduating from a so-called "dual purpose" or marine battery.