Leisure battery runs down

Hi, can anyone help a first timer?

Took motorhome to a site for the first time, everything was going great then switched on a light and the TV started to make a constant beep sound, then gradually through the evening other electrics started to fail, next was the heater, then the toilet wouldn't flush, then TV turned itself off, went to bed and the next morning had no power in the the living area except for mains sockets, motorhome had been plugged into the mains at all times, will this be a battery issue or the battery charger? Its a Fiat Autoroller 707 2012