80% is often considered standard for battery warranty. If a Mac goes under 80% in fewer than 1000 cycles, the service toolkit considers it a failure - back when I had access to pirated Apple Service Toolkit anyway. The old version for pre 2015 laptops.

I imagine it’s similar with cars. They can’t promise you retain 100% health for 8 years so they probably have some set percentage. Maybe it’s also 80%?