So I ran an experiment the last 4 months gradually lowering max charge from 89% to 55%. Once during that time the max was set back to 89% fir a trip. The degradation has lowered to 3.5% and capacity raised to 92.6 kWh. It's just interesting and I really don't know if it real. I only have Tessie numbers.
lithium ion batteries have a well documented recovery effect that means that the battery can recover a little capacity by using low SOC and cycle at low SOC.
Its not easy to set a number for the amount of recovery.
Its clear that the most part of lost capacity never comes back.
Its also clear that cycling at low SOC with small cycles recovers some lithium from fast charging (lithium plating that resolves/reverts to cyclable lithium) so when they perform research with cyclic tests and the stop the cycle for measuring of the present capacity, if they do low SOC cycles the battery recovers lost capacity.
Heres a test of actual tesla model S cells, taken from a 6 month old Tesla model S.
50-80-100% follows other research result on the spot.
But 20% is much less than it “should be”
(20 and 50% is very close in all other cyclic tests)
Why did 20% show lower calendar aging than the first thought expectation?
Well, the cells comes from a actual Tesla model S, used for 6 months. How do we think that car was charged (about 2018) ?
Well it is a good chance it was charged daily to 80-90% (as most do, and did back then).
The battery was (most probably) charged as most people do and the cells put to calendar aging test at 20% actually recovered about as much as the calendar aging caused degradation, so the end result is close to 0%.
The 50% at 25C is also less than expected, probably the same thing we see there.
So, yes when lowering the SOC we expect to see a lower degradation and in some cases even notice the recovery.
I see the nominal full pack decreases slightly when doing multiple large cycles, I also see the NFP climb when doing cycles at low SOC after the large cycles. Today I’m positive that it is the MS seeing the recovery. Its even so at it WILL climb if i do 20-30% DoD from 55-35/25% but it might stay on spot if I charge to 55% but only use a few percent each day.