I see people are yet again mixing up Tesla's sales-oriented recommendation with the scientific what is actually best for the battery. (
@TexasEV ) The thing of keeping it at 90% all the time and keeping it plugged in all the time is for customer satisfaction of always having enough range, at the cost of a small penalty of it being a little bit worse for the battery's lifetime.
Tesla does not want to have to get into these kinds of long explanations and "it depends..." kinds of things with millions of customers, so they want to have one simple answer they can have their sales people give that is a pretty good answer that works fairly well for all circumstances. It's not the best for each person's scenario, but it's good enough.
Physics is physics, so I am sure that, with the physics of how batteries work, means that there might be slightly more degradation doing that, than actively trying to charge to 80%, only plugging it in when needed, all of the "it depends" stuff.
But..
(making up numbers here, emphasis on made up numbers)
If actively managing the battery, performing a bunch of mental gymnastics to try to "optimize" the batter means the battery half-life is 30 years, and "just plugging it in" means the battery half life is 28 years, that means actively managing the battery would be "better", but irrelevant, because its unlikely anyone has the car either 30 or 28 years.
Thus, it could be "better" but "not matter" and I suspect (but have no proof) that is what is happening here. In my completely made up numbers above (for illustrative purposes only), 2 years is a statistically relevant size, but at the same time not relevant to 99% of most owners of the car.
So, if the above is something like what is going on (with different numbers of years for half life of battery), its easier and better for tesla to tell people to "just plug it in" because it "doesnt matter".
I have zero idea what the numbers are but suspect that something like the above is whats going on. I only know for my own car, I have 8500 ish miles now, drive about 80 ish miles a day round trip to work, and plug in every night with a HPWC at 48amps in my garage. I charge to 90% every night, my car reported 90% at 279 miles when I picked it up and it had 12 miles. It still reports 279 miles on 90% charge with 8500 miles.
The first month I was stressed out about "doing it right" just like most new EV drivers are (this is my first EV, unlike some others I did not move from a leaf or bolt or some other ev, I jumped in here). I went from stressed about it in the first month to 6 weeks, to just happily plugging it in when I get home and "not thinking about it" at all (except for enjoying the fact that I never have to plan to go to a gas station to fill up after work, or before I go to work).
I used to "fill up" every 4 ish days or so, for just under $50 per fill up of premium gas for my BMW 435. I had to drive that car in sport mode all the time to get the performance I wanted out of it, and I am not "boy racer". A BMW in "comfort" mode is really almost like a camry, and if you paid for a car with performance you kind of want a performance car.
My tesla gives me ALL the performance, with none of the drama or noise, and is much cheaper to operate. I am no longer stressed about the battery, or "doing it wrong" I just plug it in, and get bemused by the constant threads about "how do I do this right?"