It’s called science. Researchers performs tests about how lithium batteries behave.
There is literally hundreds of good research reports out and most of them paint a very clear and common picture. Below, facts from the researchers:
Initially we need to begin with splitting the degradation into calendar aging abd cyclic aging.
Calendar aging happens virtuallly all the time, even if the cell is constantly used.
Most EV’s are parked /stored for ~20hrs/day.
Calendar aging is set by [Time x Temp x SOC].
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(This picture could be seen as an average between quite some research reports. It is not “one of a kind but in line with the common findings.)
Calendar aging is reducing the rate with square root of time. To double the first year, it will take three more years, so four in total.
0% is
not completely empty. 0% is defined by the cell manufacturers “stop discharge point”. 100% is defined by the manufacturer’s stop charge point.
(There is research on overdischarge, and even slight overdischarge is not that bad. Not “good” but not that bad).
If you buy a lithium ion cell, for example Panasonic NCR18650 these are made to be used between 100% and 0%. It is possible to charge a lithium ion cell to 130% or so, but the life will be short. The 100% level has been sat to keep a good combination of life and energy stored.
100% is set at 4.20V per cell and is not dangerous to the cell at all. Look at the calendar aging, not really worse than at 70-90%.
This is panasonic ncr18650 very closely telated to tesla model S cells cycled at 100%, 90% and 80% (left to right)
While lower SOC reduce the cyclic wear (reducing high voltage and reducing the DoD) and is one of the reasons Tesla recommends 80% or lower, wich was ”below” 90% for very long time the 100-0% continous cycles made the cell hold up to 625 complete cycles wcich would be about at least 250K km in a LR/P.
100% - 0% will not kill the battery that soon.
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I have a lot of lithium cells since 2007. Also studied research since that.
These are made to be charged to 100%. In fact most chargers for anyone can only charge to 100%.
These two cells are two of 35 Panasonic 2170 (“model 3 cells”)I bought ~ 2 year back.
I stored them at different SOC for about one year and checked them at regular intervals. In short, they behaved just like in the first picture highest up. Actually 100% was slightly less bad than 80%. There is a lot of research supporting just that also.
One year ago I felt that the test was done so I used some cells for different tasks and gave away some. Some cells still are laying around with different SOC.
These two has been left at 100% for one year at about 24C all the time.
In short, they have now lost about 9% by being at 100% for two years. Its good damned right on that 25C line.
So charging above 90% or leaving the car at 100% will not kill the battery.
Its the two left that was at 100%.
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