I have worked on 3 different vehicles that have had between 1.3 to 1.8 volt draws with the key off. All 3 of them would drain a battery over night. All 3 of them also had one thing in common, an aftermarket radio. I tested the 2nd one in a race trailer with a solar panel. The battery was fully charged when I hooked it up, and the next morning it had 5.8 volts. It is still in the trailer. I just have to turn off a switch when I'm not using it.