I had a fancy Sterling digital controller, but found that despite the blueb saying it detected the charge state initially and charged accordingly, it always dropped into float after the same time (and too early).
I replaced the Iskra 14.0V regulator with a 14 6V one (£15 on ebay) and reckon I get a better charge than with the Sterling. I've got a fairly good idea of what is going on, with various ammeters and voltmeters. Although I don't always leave the boat with the batteries fully charged, I reckon to get about three years out of 4 x 110 basic batteries. I could probably go another year or more if I had to. This was after fitting 200W of solar panels which would top up the batteries in the 3 or 4 days I was away for much of the year.
We use a fair bit of power with fridge, largish tv, computer and phone charging, and I try and avoid the batteries going below about 12.5V.
This seems to fit with what Gibbo was saying 10 or 15 years ago. But what the hell, it works for me.