My 03 4.4i's battery goes stone dead if I don't drive the car for about 3 days. If I connect a charger to the connections under the hood, it NEVER fully charges. If I disconnect the battery cables, and hook the charger directly to the battery, it fully charges in a just a few hours.

The battery is new, and I've had it tested to confirm that it's OK. So I'm sure I have a parasitic drain somewhere. However, after reading through nnumerous posts on the topic, I'm veryconfused as to the parasitic drain test procedure. The fact that the battery is inside the car, meaning that all the interior lights are on when I open the hatch to access the battery, complicates things.

Could somebody please explain, step by intricate step, EXACTLY what has to be done to test the current drain on these cars? Please provide all details, including how long to wait between the time I get in the car (with all doors and hatch closed, presumably), and when I can start the test, how large of an ammeter I need, which cables to disconnect, which to leave connected, etc., etc. Thanks!

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT