I just wondered if it needed to fail first ?
When I bought the car a year ago it was back within a week for a new battery because of yellow low battery warnings. They checked the BSG, and it's been all fine until a year later when I've had a couple of loud buzzes not long after starting, one low battery warning - 'charge when driving', and I'm 90% sure that the stop start was greyed out after driving once ( I always turn it off).