No: polarity switching not an issue with lithium batteries. Forget that part.
100% SOC is defined by the maximum allowed voltage per cell set by the cell manufacturer (4.20v/cell for NCA and NMC)
0% SOC is defined by the lowest allowed discharge voltage, also set by the cell manufacturer.
At 0% there still is charge/energy left in the battery. Not much but enough to still be very safe.
At 0% ve have the least degradation from time for the battery. This refers to 0% True SOC.
This 0% true SOC level is way below Teslas 0% on the screen. Teslas 0% on the screen is circa 4.5% true SOC on the battery.
A NCA battery like Tesla panasonic 2170 will degrade with time according to this picture:
Its quite clear that 0% is the SOC that causes least degradation from time.
Also clear that 70-80% is about as bad as 90 or even 100%.
There is some research reports that actually points out 80% as the worst SOC for calendar aging.
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