Charging of batteries

(Moved from Social Room)

I have just read the article on "ask the expert" and noted the complaint of no replies to queries so I thought it best to ask you very knowledgeable people out there instead. Do you keep your caravan battery on charge all the time, or only when you feel that it needs a boost? I park my van alongside the garage and feed the cable through the window so have no "supply" problems there. My only concern is that I may overcharge it - what are the safety rules in this respect? Also, does constant charging reduce the effective life of the battery? Any advice would be most welcome.