Getting fed up with dead batteries, and needing a charger, I went looking round the details and talking to people who know. Eventually I have settled on a Ring Smart Charge 8. This has a battery check, desulphating setting, charges to 100% then floats. There is also a rapid charge setting.
There is a larger 16 amp version, but looking at the specs for the battrey size I'm likley to play with it wasn't worth it. The main thing that decided me on the Ring is that it has a manual recondition button. So far I've left two dead battries a 65amphr and an 85 amphr on it. Both took about two days to get fully charged but they are now holding charge and uasable.
Instructions supplied are as clear as mud, the only bitch I have with it.