I'm not worried about your charging volts , I've seen low voltages before with smart charge systems .
I'm going to do an about turn on some of the info I have posted before on finding drains , we have Vas we have Pico scope and various load rating inductive amps clamps .....they all have there uses ,Pico monitoring over long term for strange drains that can wake up after lots of hours ....it all depends on the fault that what tool you need to use .
What I have found when you are looking at drains at let's say under an amp or less, inductive Amps can ' drift ' they can be over or under the real ' in line 'drain
For your fault ,I think a basic meter inline with the battery will surfice , I use a shunt to ' tap up 'off as if you inadvertently wake the car up a big surge of amps will pop the fuse in most meters .
Roll the boot latch over , have your meter in the boot and lock the car , give it twenty mins and have a look at what amps you are pulling out , knowing what is being pulled out can give a clue as to work to start looking .
I have had instances where there has been an obvious drain I have volt dropped every fuse and not found any drop , alternators are not always fused a drain can pull through a fuse box shunt or a fet ( field energised transistor ) but they always end up back at the source .....the battery .
In some cases where positives start to branch out from battery to say a fuse plate you can lift an eyelet or pull one of the heavy fuses and issolate a whole section of take offs , if your drain stops case of looking what on that branch .
I would say it's more rare for something to power back up after shut down , it's more the case that when it shuts down there is still amps being pulled ....every instance can be different .
They can be an arse but start at the battery and work through methodically , I have been tied in knots with them over the years !
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