Mac completely draining overnight when lid closed or sent to sleep

My Mac didn't used to do this but in the past few months I cannot leave it unplugged overnight or it loses all its power. It then takes several minutes for it to get enough power to start up once it is plugged in. I've checked the activity monitor to see what's doing this but there doesn't seem to be anything stopping it sleeping. I can sit here and watch the screen sleep after 2 mins of no activity but it still just runs itself empty. I've googled and tried out several suggestions but even in this space I've found nothing that helps. Any new suggestions?

Thanks.