My understanding is they do manage themselves in that they have a margin of capacity when new which is used up as they age, to the point when the range starts to noticeably reduce. So it’s not that they start deteriorating after three or four years, they do so from new but it’s hidden from the user until the car’s warranty runs out! Of course the batteries themselves are warrantied, often to give 70% to 80% of original range after 8 years