f1geek wrote:

I don't know how to link a graph so I'll just list the data. Also, I believe that the best way to estimate degradation is to calculate estimated capacity at a constant State of Charge (SOC) because I have observed the calculated usable estimated capacity decreases as a function of SOC.

These data were measured at 18% SOC +/- 1%:

Date, Mileage, Estimated usable capacity (kWh):

7/1/16, ?, 19.5

9/19/16, ?, 19.3

4/4/17, 16,985 miles, 18.8

8/5/17, ?, 18.5

As my e-Golf is 2.5 years old (now at about 22,000 miles), assuming that it began with a usable 85% of the gross 24.2 kWh capacity (20.5 kWh), it looks like my car has lost about 1 kWh the first year and about another 1 kWh during the second year, so I expect that by the time I have to decide to buy it or turn it in at the end of the lease (next April), it will probably be at around 17 to 17.5 kWh usable capacity. That's about a 5% capacity loss per year.

The VW battery warranty is 8 years or 100,000 miles against 70% capacity. At the rate my battery is losing capacity, it seems the car would get a free battery from VW at the end of 2018 or in early 2019 as 16.5 kWh usable is equal to 68% capacity. It will be very interesting to see how many battery packs VW replaces in 2019. Maybe they'll be the new 35.8 kWh pack? Only time will tell.

I suspect that you're doing the math wrong with respect to the 70% warranty. I would expect VW to calculate the usable capacity at the time of claim and then divide it by the usable capacity when new. So, using your own numbers, 16.5kWh / 20.5kWh = 80.5%. So, that would not be a valid claim. My thinking is that the battery would have to drop from 20.5kWh to 14.35kWh before you could make a capacity claim. If the battery is truly degrading at 5%/year, then you could make a claim before the 7 year warranty runs out. However, you can see in my chart above that the Blue linear fit line has a slope of -3.75%/year. If it is truly linear and that is the correct slope, that would only be 26.25% after 7 years.