Nice guide! I just did mine the other day (and coded)!
Very simple to do, and fyi, you do NOT have to use a "BMW" approved battery. That is totally up to you! The only difference you would need to worry about is the AGM and non AGM type when it comes to registering it. I had the stock non-AGM, 720CC 160RC (original battery), and I replaced it with a Duralast Gold Battery (H8-DLG, 760CCA 150RC) from Autozone. It costed me $140.
