Model X 100D Battery Internal DC Resistance

[lymex2018]

Several days ago I’ve driven on a mixed road including hi-way for 48km and recorded the data by Scan my Tesla.
After I plotted the chart I though why not calculate the internal resistance of the battery.

Extract an 8 minutes section data when the power change seems to be the most.
Modify the voltage to compensate the gradual drop because of the SOC changes assuming 4.2V for single cell at SOC=100% and 3.0V when SOC=0%.
Plot a scattered diagram in Excel and adding a red trend line and display the equation and R square:

Immediately we can see that the internal DC resistance is 46.1 mOhm and R square = 0.987 giving a good confident.
Considering the pack is 86p96s, minus about 10% of wires, fuses and contactors, the internal resistance of each cell would be roughly 46.1*90%*86/96 = 37 mOhm.
I also extended the trend line forward.

 

[lymex2018]

Add:
Battery DC internal resistance varies with several factors such as temperature and degradation.
Low temperature has great influence to the internal resistance which can be seen from the discharge curve. The temperature was 36.7C (body temperature) when I did the test. My car is also relatively new and the mileage is about 3000mi.