It would appear that you have a parasitic leak. It could be any one of a number of things, i.e. boot light, radio, interior light etc. Best to have a parasitic leak check carried out. If it shows a leak, then you will need to remove one fuse at a time to identify the problem area. Have attached a link showing how to do this: www.popularmechanics.com/cars/car-technology/a5859.../