Battery Charging/Power Supply Issues

Hi - my first post motivated by some rapidly worsening power issues in my 2008 Sterling Europa 540. It started on a 2 week trip after accidentally leaving the awning light on all night. This drained the battery down to sub 9v according to the caravan battery meter. Given that I was on electric hook up and all 240v were working I was somewhat surprised.  A further symptom of theproblem was the fridge registering there was insufficient power to operate - given I was on EHU and the fridge was set to mains. There were no apparent fuses blown and with a charge from a Halfords battery charger we were back on track although with less than normal power (12v). 

On a subsequent weekend away even with EHU it appeared that although the mains were all working the 12v circuit was draining the power from the battery and it was not re charging so every time we switched a light on or ran the water pump the voltage decreased. So again the halfords charger  was deployed (it is the model designed for caravans) which got us through the weekend. However just four days later when I went to move the caravan with the motor mover it was totally drained - not a thing registering and the charger won't even charge the battery now. 

So - a couple of questions?

Does anyone know why the circuit and on board charger seem not to be working and what is the solution?

Now the battery is not taking a charge is it recoverable or time to get a new one? If so I don't want to get a new one until I know the on board problem is solved?