Trouble is the bmw cars with this engine has the same. Maybe the OS module requires it.
It would be interesting to know if any brave would has gone the cheaper route
I would suspect the charge parameters built into all the BMW electronics and the alternator are set up for an AGM battery, you can't even swop some batteries like for like in 'moderns' without a laptop reflash
RichardV6 may chip in with some sage advice...
