It is not about how many KM you have on your car, it is about how far you drive on each trip. My battery was replaced under warranty because I bought a CPO M3 and the car sat in their lot for around 7-8 months. So pretty much 2 months after I got the car, my clock was slow and since it was their fault (car sitting in the lot for a long time), they replaced it under warranty.
As Jaypod mentioned, no matter if they are right or not, it seems like that they did not treat you right.
AW|FR 6MT E92 ///