Battery drained over night?

i have a 2009 chevy cargo van and about a month ago the battery was going dead over night.i am in expediting and i am running the car more than 5-6 hrs a day. i tested the baterry with all accessories disconnected, the alternator it is charging the battery, checked the fuses, etc. the only way is to disconnect the battery over night and when i have to get back on the road just connect it back and the van starts.i took it to a few shops i got charged and the same answer. something is draining the battery but i got nu fixes from any of them. what i know is that the negative cable draws more than 1 amp. on my tester it shows 1.40 for example and then keeps goin up till about 19. something and after that only shows a 1. and in the book that 1 or -1 means that the reading is bigger than the amp tester is able to read. it has a 10amp fuse. i am out of options. and i paid almost 500 $ to all the shops for no reason. any suggestions? thank you all.