> For batteries, 80% of the initial capacity is referred to as the point

The publication cites sources from 15 years ago for this "fact" [0]. That's ancient history in the context of EVs (even before the first reliable mass production EV - Tesla's Model S - was initially released). As a practical matter, the article points out that most EV manufacturers (Tesla included) warranty their batteries for at least 70% capacity at timespans near a decade, which would bankrupt them all if EV batteries just up and died at 80%.

0) [35] O. Erdinc, B. Vural, and M. Uzunoglu, ‘‘A dynamic lithium-ion battery model considering the effects of temperature and capacity fading,’’ in Proc. Int. Conf. Clean Electr. Power, Jun. 2009, pp. 383–386.

[36] K. Smith, T. Markel, G.-H. Kim, and A. Pesaran, ‘‘Design of electric drive vehicle batteries for long life and low cost,’’ in Proc. Accelerated Stress Test. Rel. (ASTR), IEE Workshop, 2010, pp. 6–8.

It is an older paper, though that in itself isn't a reason to discount this (or any science). For example, the DoE still uses an 2014 predictive model to estimate longevity of today's EV batteries at "12 to 15 years in moderate climates (8 to 12 years in extreme climates)" [1]. However as the DoE says, battery longevity depends on a bunch of factors e.g. chemistry, charging patterns, etc.

To the practical matter - yes, EV manufacturers are very careful with warranty periods. Anecdotally, an acquaintance had a Tesla for 8 years. 6 months after the 8-year battery warranty expired the battery ceased working. The details were a little unclear (it was explained in broken English/Norwegian). That said, anecdata carries little weight. What we need is more peer-reviewed research to update our understanding of battery longevity. Until we have that we need to rely on the existing published knowledge... otherwise anyone can assert anything and we learn nothing.

[1]: https://web.archive.org/web/20250530000446/https://afdc.ener...