For the Tesla batteries, here is the most comprehensive study I have seen
From Green Quora:
"The data appears to show that capacity remains between 90 and 95 percent, on average, even at 150,000 km (93,000 miles).
But, overall, the data offer some basis for confidence that a Tesla Model S will lose—on average—less than 15 percent of its battery capacity over the average 150,000-mile (250,000-km) life of a vehicle."
I STRONGLY suggest anyone that actually will own an electric vehicle read this article:
https://steinbuch.wordpress.com/2015/01/24/tesla-model-s-battery-degradation-data/
From the article:
"The red fitted line has a slope above 60.000 km (say 40,000 miles) of 1% per 50.000 km (30,000 miles). On average the batteries have 91% remaining at 270.000 km (170,000 miles). If the linear behavior would continue, then the ‘lifetime’ (still 80% capacity left) can be calculated as follows: 91-80 = 11% times 50.000 km = 550.000 km, plus 270.000 km, gives 820.000 km (510,000 miles)! "
I would expect the newer Tesla's and especially the Porsche batteries with a more sophisticated temperature management system, to last even longer. Temperature is the number 1 cause of degradation of batteries.