Another independent self reporting study is available about the battery life of the Model S. This new data again shows that the Model S batteries are holding up well. The average Dutch Model S owner with 30,175 miles reported a rated range of 238 miles on a 85kWh battery.
From the Netherlands, Merijn Coumans is maintaining an ongoing record of the Model S battery life. He has gathered his information via the Dutch-Belgium Tesla Forum. You can access the file yourself. This data contains information from 109 owners. All but five owners reported results recently with firmware 6.0 or higher. Only six of these owners have a 60kWh battery. None of the European Model S cars have the A battery, and all but five owners reported results on version of V6.0 software or later. For more charts and analysis, you can read a report from my fellow blogger, Maarten Steinbuch.
I had done a similar survey in 2013 with similar degradation results over time. My goal for that survey was to determine if driving habits had much influence on rated range. The survey debunked that rumor.
This second survey again shows two main facts. First the Tesla batteries are holding up well and only degrading by an around 6% at 50,000 miles.. Secondly, measuring this data on your own car is a bit challenging as there are several things that can affect the number. How recently did the car have the battery drained to near zero and filled back up completely? On my cross country trip last spring I noticed my rated range go up as I had fully charged the vehicle several times.
I have now switched my car over to display a % number of charge left not the rated range value. I have really no concern about battery degradation at this point.
TESLA OWNER 
Great survey. I was expecting pretty good battery life in all upcoming models than what we had got now.
The predicted range on my car went from the 260’s to the 240’s after an update. This was over a year ago in one of the 5.x updates. I thought they adjusted how the calculate the estimated range to cause this. Since then it has not gone down at all, a full charge still puts me in the 240’s. Hence, I don’t really think there’s any significant range degradation so far. I’m at 28k now, after 24 months of ownership.