Caravan charger

hi folks, e have a compass omega 524 and having an issue with the battery, the caravan has not been used until covid started, and my friends daughter was made homeless, so we lent them our van, in the last week the battery has gone flat totally, getting no power for the lights or for water pump, van is getting electrics in, i have got the battery on charge now to see if its charging and holding a charge, my friend is coming round later to check the charging unit is getting power, and if it is, is it putting power out to charge the battery, if it the charger thats faulty, any one have any ideas what to change the charger unit to if this is where the fault lies, under the seat at back of the battery box is a box of fuses, and i have checked everyone of them, and all fuses are ok, would there be any other fuses anywhere if i find power going into the charger, but no power from it to the battery, trying to rule out what might be wrong first, 

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