Renault review: battery fault renault master 161d40884

i purchased the above vehicle from Michael Grant Motors Sandymount on the last visit with them i reported that the van seemed to be a bit sluggish to start they ran a test on the battery and said that it was faulty and needs to be replaced Under Warranty however they did not have the correct battery in stock and would change it at a later date
I have also called Renault assist to this issue they to have said that the battery is not holding it charge and is faulty
The vehicle is currently been serviced at Airton road Renault they have said the battery is not covered under warranty but needs to be replaced at a cost of over 300euro
I have tried to call several times today to but cannot get to speak to anyone