The graph is based on displayed range for a 100% charge. But here in France with a lot of tests with friends, we seen that the value displayed can be far of the reality.
The range displayed is based on the estimated capacity of the pack, and in some condition the car cannot precisely knows the real capacity of the pack. For example if you never charge charge to 100% and go close to 0%, the computer cannot knows exactly the energy stored in the pack, and update its internal data.
For example, I have my car since 16 month, 35,000mi , it's a "D" pack, and I am very careful in my use of the car to keep my battery in the better health as possible. On daily use, I never charge more than 70%, and never discharge below 30%. And when I need to do a full charge, I calculate the charge to finish just before I go.
And I found that when I only charge at 70% for a long time, my range decrease gradually. Some month ago a full charge gave me a typical range of 226mi (364Km) !!! But after vacation and some trips with long range with SoC close to 0% and charge to 100%, the computer estimation for a full charge increased to 232mi (374km). It's a 2.7% better range, and was just a computer deviation, not a 2.7% battery degradation.
A friend has the inverse case, he is taxi, and always charge its car to 100%, and the car sometime stays very long time at this 100% SoC. It's very bad for the battery, but its car display a typical range of 252mi (406km) !!!
We all had a doubt on the reality of this display, and we was right, 2 time the car completely stopped with 5mi range left on the display !!!
Compared to me, when I arrive to 0mi left, I have 3kW reserve available from the pack before the car completely stops.
Thus to compare the battery degradation in a precise way, it's not possible to use the displayed range. The only precise way is to regularly (for example 1 or 2 time a year, when temperature is close to 20°c) do a full charge, and drive without big acceleration and with a low consumption until the car completely stops. And look how many energy (kWh) you was able to get from the pack (also note the value when you arrive to 0mi, it's interesting to see the reserve energy).
And the best is to do this in a single trip, because if you stop the car the vampire losses will not be taken into account.
It's what we call in France the "Rolland" protocol (it's the name of my friend who exposed the protocol) :biggrin:
I do a complete discharge 3 week ago (not really complete, because I have not driven until the car stops, but when the power limitation was just under 60kW, but I was really close to the end), and I was able to output 69.9kWh from the battery when I reached 0mi left, and 3.1kW more until to be very close to the car stop warning).
Thus 73kW total. I will probably able to output a little bit in better condition, temperature was lot, and I have not driven in an economical way...)
And 69.9kWh before the charge now message should correspond to a full typical range of 235mi, and my car actually displays 230mi, thus 2.1% less than the reality, again it's not battery degradation it's just a computer error.
It can be very interesting to create a topic to follow the evolution of the battery capacity of all user who want to regularly do this measurement