Battery going flat in less than three days.

I have a 2010 Sterling Elite Explorer & am having a problem with battery life. I'm sure that I must be doing something wrong but the battery (110amp leisure battery) goes flat in around three days. I carefully switch all systems off & this still happens. This makes using the caravan for stand alone weekends impossible. All of the interior lighting is modern factory fit LED which I assumed would be a boon but it is not to be. I have replaced the battery which was less than two years old & it made no difference at all. The on board battery charger brings the battery up to a healthy charge but as soon as the mains are switched off we go back to stone dead battery in the usual three days.

All advice will be gratefully recieved..