I have hooked up a deep cycle battery to my sprayer trailer to run the electric reel. The battery is hooked to the electric reel motor through a switched relay. The problem is that my main truck battery has been draining everynight since i have installed the extra battery. However, my rudimentry, but I beleive sound, understanding of 12v electrics doesn't support this. There is no reason for the trailer battery to drain the truck battery -- that I can see. Even if my trailer and truck are sharing a ground through the hitch -- it still should not drain my truck battery right? But... what if the relay or the motor on the trailer are drawing a small current? COuld that cause a drain on my main truck battery -- I don't think so -- but maybe? Any thoughts?