The battery capacity drop is measurable.
Bjørn Nyland released another update on his Tesla Model X battery degradation after 75,000 km (46,600 miles) on the second battery pack.
In short, available battery capacity decreased by some 6%, while at 35,000 km (21,800 miles) it was 3%.
Details after 191,457 km (118,991 miles):
- First battery pack was replaced after 116,000 km (72,000 miles) under warranty.
- Second battery pack - 82 kWh (new) 35,000 km (21,800 miles): 79.3 kWh (down 3%) 75,000 km (46,600 miles): 77.2 kWh (down 6%) - 368 km (229 miles of range) assuming 210 Wh/km
Bjørn tries to explain the 6% battery capacity drop due to his specific driving profile with a lot of high-load driving with a trailer and many Supercharging sessions, which increases battery temperature and probably accelerates capacity fade.
Overall, even if the capacity fade is higher than average for Tesla, the capacity and range is still high enough to not be of a concern to most drivers.