My w203 220cdi battery is constantly going flat. It doesnt hapen within a few hours but if left for over about 8 hours or so it will start to show signs of strugling to start and any longer than that it doesnt start at all. Been on star at mercedes and it is not any sams. I also found out that interior light was causing a drain so removed fuse for that and that seemed to help a little but it is still draining power from somewhere. Could someone help with any info of what it could be, thanks.