FSU definitely bypasses any attempt of battery management. If you haven't ruled out FSU definitely unplug that sucker

You can't reality do DIY on BMW without a proper scan tool. The cheap painful route is the free software and old crap top The far less painful way is foxwell 510/520 scanner you can often get on eBay half price

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)