OH but if you have to leave the batt unattended, then you just need to think about what will be easiest for you to recharge the batt in the future.
do you have the option to charge the batt while in the vehicle, OR is it easier to charge the batt if its sitting on a bench?
Only reason I say, is cause after 3 months, the batt will 99% be dead, and you may as well just leave in the X and charge it when time comes, instead of removal/re-install of it.
Just make sure, as "mywidebody02" said, to keep doors unlocked or a tail gate open to ensure access to batt (if removal/re-install is way you go).

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S