eyemgh wrote:Maybe, more importantly, a drive to 75% SOC from full and multiplying by 4 should give a pretty accurate estimate of true range shouldn't it?
Range in a test drive is not the way to compare cars, since the driving conditions will not be standardized. What you really want to know is the pack's energy capacity, which is analogous to the fuel tank size in an ICE car. "Range" is simply the capacity (typically in kWh) times the specific "fuel" mileage you are seeing (in miles per kWh).
If you drove at a constant 90 MPH, your car's range would be MUCH less than if you drove at a constant 40 MPH because aero drag goes up with the square of speed. Similarly, if you were going up and down hills, with stops every block (think driving in Pacific Heights, San Francisco), your range would be less than driving in a flat region with few stops, because regeneration is not very close to 100% efficient. So, range in a test drive alone isn't going to tell you anything of much use for assessing the car's health. If the test driving conditions mimic your intended use very closely, I guess you would see how far you could go, but you would not know how "good" that car's battery is relative to others.
In principle, you can measure the pack capacity by the following method: reset all trip computers and energy histories on the dashboard and the center nav screen system. Shut off car and turn it back on to zero LeafSpy readings. Note the SOC % shown on the dashboard and in LeafSpy (which probably won't be the same, so record both). Start driving for as long as possible. You want to knock the SOC % down plenty. Fifteen to twenty miles of steady highway speed would be good; out and back along the same road so the vertical averages out but flatter is better so you don't have regeneration throwing off things. Stop and note the ending SOC % on the dashboard and in LeafSpy. Also read the mileage in miles per kWh from the dashboard or nav screen, and from LeafSpy (it's on the Summary screen, and you have to poke the little block of text above the colored bar graph several times to cycle through to it...take the Trip one with only one number, not the Charge reading with two numbers, one in parentheses.) Subtract the ending SOC from the starting SOC. Say they were 78% and 53%, so the difference is 25%. Divide that number by 100%, so the fraction of the battery you used was 0.25. Now, how much power did you use? Say you drove 19 miles at 3.9 miles per kWh. 19 miles / 3.9 miles/kWh = 4.87 kWh (energy consumed.) Divide that number by 0.25 and you get 19.5 kWh as the total capacity of the pack, which would be pretty good for a several-year-old car. I think my car holds abut 18.5 kWh, and it just lost its first bar.
I should say that, while this sounds good on paper, I'm not totally convinced it's foolproof to do this on one test drive and say you "know" the capacity of the pack. Mine actually got a better score on my first try!