Motorhome engine battery

Coalman

Hello i need help regarding a motorhome engine battery.

I own an Elddis signature 165 motorhome and i have left it at a freinds house due to my work commitments he has been starting it up every 2 days. He went to start it up 2 days ago and nothing, He said a lot of lights came on on the dashboard and the battery
didnt have the strengh to open the door, this is the second time this has happened.Do you think its the charging system that is faulty or battery itself.The van is a 2013.