Dave's recent post reminded me that I wanted to ask about this graphic that AAKEE posted. It seems to show a sharp break between aging about 55% and lower, versus aging at 60% and above. The text to the right of the graphic seems to address this a little, but, it's hard to read since it's cut off.
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Can anyone explain what is happening in this region?
I’ve been thinking about this and AAKEE’s posts a bit more. AAKEE pointed to a really good study here:
If you go down to section 5.2.1 (page 50), they have a similar chart/graph but out to 700 days or about 2 years. They tested calendar aging at 15%, 75%, and 90% SOC, and at 25C, 35C, and 45C.
Reading the graph, I’m concluding two things: 1. At 25C there was no appreciable difference in aging between 75% and 90% SoC. I.e. If you’re in a moderate climate, then the difference in battery calendar aging of 75% to 90% SoC is minimal to zero, maybe not worth dropping the charge down.
2. At 2 years in, the 15% SoC appeared to be at 98.5%-99% capacity, while 75% (and 90%) @ 25C appears to be 94.5%-95.0% capacity. Perhaps the inflection point is 55% as per the study above. If that’s linear over time - then at 10 years you’re looking at 5%-7.5% loss staying at 15% SoC, and maybe 25-27.5% loss at 75% or 90% SoC. (At 5 years the losses would be about 3% and 13% respectively).
It feels like if you’re going to keep the car for 5-6 years, I don’t see “3% degradation vs 13%” making much of a difference in resale value. For road trips at 5 years old, the 10% difference probably is tolerable too.
However, if you are keeping the car a lot longer - 10 years or more; at 10 years you probably also don’t havre too much difference in resale value - because 10 year newer EVs are going to be much better (and cheaper) in the battery department.. It’s going to be hard to trust that battery degradation really is low on a 10 year old vehicle even in the face of evidence, and “feeling” about a car tends to determine it’s price at that age. OTOH a road trip in a 10 year old EV with 25-30% range loss is huge vs. one with 5-7% range loss.
(I normally keep cars for 12-15 years myself (until they’re basically costing a lot of money and time to maintain), but with EVs improving so much every year especially over the next decade, I might revise that. Sell the 4-5 year old EV while it’s still worth something or similar. )
All this said I’m still thinking about limiting to 55% SoC based on the data above going forward to prevent further degradation of my 3…