My car is almost 27 months old, and it has 17500 miles on it.
I have very little battery capacity loss over that time, I still get standard mode charges of 189 miles and range mode charges of 240 miles.
The community here at TMC provides us with a great opportunity to learn more about this issue.
I worked with Tom Saxton to add some features to his log parser. It is available here: http://www.idleloop.com/tesla/vmsparser/
If you run "VMSParser -b *.tar" and pipe the output into a text file, it will record summary data so you can make histograms for the following items:
1) charging amps
2) state of charge
3) ESS temperature
4) brick ah capacity average
5) time range covered
No GPS, speed or other identifying data is in the output.
Note that the interesting data is in the temporary section of the log file, so if you do not have a steady stream of log files ( one every 4 or 5 months ) then there will be some holes in the data but it is not a fatal problem.
If a great many owners from our community would be interested in getting the log parser, and generating the data and sending it to me, I will try to analyze it and look for correlations and relationships among those variables and battery capacity. It's very likely that I will add more variables to the parser and reissue it and ask for new data.
As soon as I have any interesting findings I will report them.
To send me the data, please just email the text file to teslalogdata at gmail dot com, please add the ideal miles you got at your last standard mode charge and range mode charge if possible.
Here are the histograms ( courtesy of Excel ) from my car:
The first is ESS temperature in C
The second is charging amps in hours
The last is state of charge in % of time
Some possibilities in the future:
1) divide temperature into idle, charging, driving
2) divide soc into idle, and driving
3) add ESS power output
4) complicate it all by adding a dimension: state of charge vs temperature