i agree with you D5K2, the number of charge cycles is a good measure of battery life--there is a curve on the panasonic cells that shows the capacity loss versus number of cycles, it seems that nearly all the battery manufacturers show that same sort of curve.
i would guess that tm has that info stored somewhere in memory. Apple's macbook will display number of cycles on the battery when you click the apple About this mac/system report/hardware/power. kb
All this is obviously true. There is a big "however" though that nobody seems to be thinking about in this thread. Li-ion battery pack behaviour varies enormously with chemistry, manufacturing techniques, assembly techniques and equalisation, as well as all the other factors being discussed here. From both unofficial and official sources we know that Tesla cells, batteris and packs are all materially different than any others being produced. We also know that material changes are being made in several crucial areas both by Tesla and by Panasonic.
So, anything we say about battery life in our cars cannot be a simple extension of other li-ion performance, nor even of prior Tesla history. Our tesla packs are now probably good for eight years and about 100,000 miles, more or less, with 80% or more capacity at the end. Will any precise measurement of residual capacity be available? No! The deterioration curves of lithium chemistries all seem to have been remarkably consistent; an initial sharp capacity drop (often pre-performed prior to customer delivery) followed by quite long stability with gradual drop, then a sharp drop commencing just prior to failure. The problems are dual; First, precise in-service capacity measurement cannot be made without harming cell service life, so various algorithms are used to estimate capacity. Second, effective service life has been increasing rapidly for nearly all lithium chemistries, but each improvement also introduces new question about service longevity. All anybody knows is that it is improving, and for Tesla probably more than most others.
Improved Performance of the Silicon Anode for Li-Ion Batteries: Understanding the Surface Modification Mechanism of Fluoroethylene Carbonate as an Effective Electrolyte Additive - Chemistry of Materials (ACS Publications) is just one recent example of published developments
Theoretically we might guess that the 90kWh packs might have shorter life because they have introduced at least some silicon in the anodes, increasing capacity but also challenging shorter anode life. There is plentiful published research on this subject, and additives of various types are reducing the negatives:wink: It seems Tesla/Panasonic are well advanced in solving these problems and may well have some substantial further improvements in service life, energy density and manufacturing cost reduction coming within the next year or two.
We need not be much preoccupied as users, IMHO.