This derating is actually really easy to implement: a standard lithium ion cell is actually fully charged at 4.2V, but the battery management system will report it as fully charged once it reaches 4.15V or so.

For aerospace they only go up to 4.05V, and the cells last tens of thousands of cycles with less than 10% capacity loss after a decade:

https://www.nasa.gov/wp-content/uploads/2024/01/saft-ves16-c...