OP, I think you have more than enough info here lol but as you are only parking the car for 2 or 3 months, I just snake the cable of the trickle charger in near the hinge and connect it to the points identified in the manual. I'd fill the tank with quality gas and call it good.
I had a friend park his M4 (I know it has a different battery) for almost 7 months and it started with the first turn of the key.
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'17 M2 DCT Long Beach Blue
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