leisure battery not holding charge

Hi i have an autotrail excel 600b purchased from new in 2010. I have had a problem with the leisure battery holding its charge. the motorhome as a EC225 power control system. It charges fine when on the electric and we go away with fully charged battery on arrival at site which is normally a field as my wife runs agility dogs and not all venues have electric hook up. we get set up and then just check battery level which reads 75% full and yet we have not turned anything on. I have also noticed Vehicle battery as same reading. on the ec 225 have noticed there is a 5amp fuse permanenet supply for radio and fridge when i checked the fuses i noticed that as i pulled it out it was live fuse o.k. Does anybody have any idea as to wether this should be so as i assumed that everything would be off when not in use. the battery we have now is the 4th this was purchased in march this year. wondering if the control panel might be defective? Power control system as been checked and is charging ok as is alternator. Sorry if this is long winded ust hope some body can help