My battery died about 6 months ago and it's my DD. However, I drive very little since I don't commute in it.
It seems that there are two OE batteries that's used. A black one with vent tube and a white one without. My black AGM battery that came with the car died and BMW just replaced it under warranty when I went in for other warranty items. I didn't even ask for it. It's white without vent tubes.
It's 3 10mm hex nuts on top of the cover to reveal the battery, then disconnect the +/-, it's out. 10 minutes with a 10mm socket.
HTHs,
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