Dave Plowman (News) presented the following explanation :
You need to make sure everything is allowed to go to sleep mode before
measuring the quiescent current.

I agree, some electronics wake up, even with just a slight change in
voltage across them.

3.6 amps would run the battery flat in less than one day.

A normal figure would be more like 0.03 amps (30mA)

My car, loaded with electronics, sleeps at 20mA, with an odd higher
short pulse, which I assume is for the alarm system.