Here’s an example of a 2016 Model S 70D with 29k miles that I pulled the CAN bus data from:
100% charge advertised miles (new): 240
100% charge rated miles: 217
217/240 = 90.4%
If I’m just using rated ranges to try to estimate battery degradation (which I don’t really recommend), this would suggest this vehicle has a 9.6% degradation in battery capacity.
New kWh: 70 (assuming software limits exactly at 70, since it’s actually a 75 kWh pack)
Current kWh: 67.3
67.3/70 = 96.1%
I have no idea how the estimated range works, but I’d imagine it does take some factors into account over time and will adjust based on whatever algorithm Tesla is using. We’ve also seen users report different estimated ranges after updates, which I suspect is from an update to that algorithm.
Side note:This vehicle was showing the displayed percentage being ~3% higher than the actual state of charge (coming from the CAN bus). Normally, the actual state of charge is ~4% higher than the displayed percentage, so I’d suspect the vehicle would actually shut down before reaching 0% indicated. This would be an example of where letting the battery get to a low SOC then charge up to 100%, repeated a few times, might help resync the displayed battery percentage.
Bottom line, I probably wouldn’t worry too much unless you see a sudden drop in displayed range or abnormal battery behavior. If you really want to know the degradation, you would have to measure the total capacity when it’s new and compare it against current capacity.
Correction to this post I made previously. Based on some new stuff I've learned, I'm convinced the displayed rated miles is simply the reported "Nominal Energy Remaining" multiplied by the EPA Wh/m. For example, the last time I charged my 85D to 100% it was reporting Nominal Energy Remaining of 76.0 kWh with 262 displayed rated miles. The 85D uses 290 Wh/m for its EPA range, so 76000/290 = 262.0689. I'd say that matches (almost) exactly with the 262 displayed rated miles.
Why the displayed rated range can change depends on a few things:
1. This is obvious but battery degradation. As BMS reports a lower "Nominal Energy Remaining", you'll get lower rated miles displayed.
2. Changes to the algorithm. Can't prove this one, but there's been reports in the past of the displayed rated miles changing after an update. Doesn't seem unrealistic to think they've tweaked the algorithm over the years.
3. Your car doesn't always charge to the same kWh at 100%. For example, my car reports a "Nominal Full Pack" of 76.3 kWh but as I mentioned above when I charged to 100%, "Nominal Remaining" was 76.0. Doing the math, it's pretty clear the car is using Nominal Remaining to calculate the displayed rated range. I'm thinking if you charge to higher SOCs frequently or recently, you'll probably get closer to a "full" charge. In my case, I don't know when the last time it was charged to 100% so not only did it take forever from 90 to 100%, it also only charged to 76.0. I suspect other variables are also a factor, such as temperature. Bottom line, I think the reason you might see some variability in the displayed rated range at 100% SOC is because the actual kWh, Nominal Energy Remaining, isn't always exactly the same value.
So, is using rated range an accurate way of measuring battery degradation? I think it is with a little bit of variation based on what was mentioned above. My example in the previous post I think was flawed because I didn't check the Nominal Energy Remaining at 100% SOC. Anyways, just wanted to correct myself incase anyone reads these posts in the future.