Qsilver7, i will go take some pics now. As i am putting my new bmw h8 batt in now anyhow
So once i remove the metal 10mm nut and metal triangular tab which holds the batt down there are also 2 pillar like structures molded into the batt tubs base (showing in red circles in pics a few posts down from this). These triangular pillars are in lower right corner and stop an h9 batt from fitting
Also on the left side of the batt tub there are 4 or 5 plastic hold down fingers too that stop an h9 from insertion (showing in the red rectangle in the pic a few posts below this one).

Note the pics showing the physical dimensions of the tub on my 4.4i. Maybe the 4.8iS has a larger tub?

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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