"How to Test and Find a Parasitic Battery Drain (Key Off)"/ battery drain
 

"How to Test and Find a Parasitic Battery Drain (Key Off)"

I did not like the guys persona in this vid but he puts out the info in a logical and effective manner.
I knew how to do it but watched the whole thing and I did learn that vehicles can have more than one fuse box which I did not know.

https://www.youtube.com/watch?v=zdIKNnwEjIs

This method is kind of incorrect for any new car, The correct way is to test the voltage drop across the different fuses.

btw - welcome to the new era - cars now have 3 or 4 fuse boxes and some are hidden too. While some are control modules themselves.

I regularly get some vehicle for such testing, and find out that someone spent hours and hours diagnosing it this old fashioned way. Not calling them incompetant but rather uninformed. Newer cars have control modules that will wakeup other modules if you start playing with their fuses, and if the ignition is left on for too long, then it can deplete the battery which throws off the test and can cause the systems to go into safe sleep mode.

so best way is to put a "power supply" on the car that can support all the load it can put on, let the car sleep according to the manufacturer and then start probing the problem. The power supply I mention is not a battery charger, I use a junked server power supply that can support upto 70 amps of draw at 12V.