Frankly I think all these methods miss an important point, which is that battery degradation is not factored in.
At 80,000 miles, the batteries will likely only be running at 70% capacity and once they fall below 70%, it is likely that cells will start to get close to failing.
This means that the true cost per mile would have to include the loss of capacity on the battery.
Here is an example of how that works. A friend of mine bought a Nissan Leaf about 7 years ago and the pack was so bad that her mileage was half, and then she started to get error codes. Since the batteries were going bad, their choice was to just sell the car really cheap and let the new owner put in new batteries, or put new batteries in it. The car was in pretty good shape otherwise, but they elected to sell it and only got $5000. A new pack, installed, would be $6500.
So, any cost estimate that does not include battery depletion is not really capturing the true cost, which is going to show up at re-sale time. A car with a worn out pack is going to be worthless.