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Charging

DerbyDave

Active Member
Jul 2, 2020
1,288
783
Kentucky
Unless you are going on a trip, there is no need to charge daily above the maximum of your normal driving, plus whatever you need for emergency buffer, unless you live in an area that has frequent or seasonal power outages.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
6,807
8,423
Boise, ID
There is a reason why the display on the car shows the whole area from 50% to 90% as "DAILY". Toward a middle state of charge is healthier for the battery long term, with less degradation of capacity, but that's not a very practical way to use a car, so you will probably need it high enough to have reasonable distance to use without worrying about it all the time. So you pick some area that works well for you. Some people find this compromise around 70 or 80% if they don't always need a lot of driving range every day. And no, that doesn't require reading volumes of battery studies.
 
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ucmndd

Well-Known Member
Mar 10, 2016
7,036
13,822
California
Are there any pros and cons to charging my model S battery to 90% every night? Tia.
I have 120,000 miles on my car, almost all of them the result of 90% at home charges. My battery degradation is at about 11%, which is a little high, but not out of the ordinary and plenty of people are seeing the same figures at less miles or with charging habits some regard as "better".

There's really no reason not to. 90% is fine.
 
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ATPMSD

Member
Mar 12, 2021
350
358
Atlanta, GA
FYI

Life vs SOC.jpg
 
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ucmndd

Well-Known Member
Mar 10, 2016
7,036
13,822
California
...except for this:
As I mentioned, it’s no higher than lots of other reports from the same vintage 75kwh cars, some with less than half the miles, from people who claim to participate religiously in all the “battery health” charging lore and hocus-pocus.

So I’d treat any claim of causation there pretty skeptically.
 
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ucmndd

Well-Known Member
Mar 10, 2016
7,036
13,822
California
You misspelled the word "data".
If the data isn't observable in real world fleet conditions, and doesn't account for the other variables that obviously have a significant impact, does it matter?

Tesla obviously thinks daily charging to 90% is just fine. If you need the range, or want the reassurance, do it, and don't waste another minute fretting about it.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
6,807
8,423
Boise, ID
If the data isn't observable in real world fleet conditions, and doesn't account for the other variables that obviously have a significant impact, does it matter?
And yet it is, and it does, so it does.
Tesla obviously thinks daily charging to 90% is just fine.
Tesla is trying to sell cars, not protect batteries. They want to encourage people to have enough range to not have range anxiety. If 90% were so perfect, as you are implying, they wouldn't even bother to have an option to set it lower than that.
If you need the range, or want the reassurance, do it, and don't waste another minute fretting about it.
Sure, if having extra range is a more important priority at times, then people should be willing to accept a bit of extra long term degradation for that practical use. And I LOVE how people think it's "fretting" or "stressing" or "worrying". It's not. I'm aware of it and know what it does, but it's set it and forget it. I picked some number less than 90% that works for me, and don't "fret" at all about that.

These are not hard concepts. I'm not sure why you are trying to be so antagonistic to people having data and making decisions based on that.
 
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ucmndd

Well-Known Member
Mar 10, 2016
7,036
13,822
California
I'm not sure why you are trying to be so antagonistic to people having data and making decisions based on that.
I don't see anything particularly antagonistic in any of my responses, but I suppose I could start passively aggressively marking your posts as "funny" too if it would be helpful to the narrative.

You suggested causation between my regular 90% charging and observed degradation. I maintain that causation doesn't exist, or at minimum would be extremely difficult to prove, and suggested there are many available counterexamples and variables at play - lots of which are discussed in this thread: What's your S 75 range at 90%?

Yes, on a bench test in perfectly controlled conditions, a lithium cell that is kept between 65 and 75% over thousands of cycles last longer than others with larger duty cycles. This should be surprising to nobody, but as you mentioned would make for a pretty poor electric vehicle experience. In the real world, with so many other factors at play like temperature/cooling, charge rate, cell imbalances, BMS capabilities, depth of discharge, rate of discharge, etc etc etc playing out over tens or hundreds of thousands of miles, I don't think anyone can point to any "data" and state definitively that regularly charging to 80% instead of 90% makes any meaningful, reliably measurable difference as to the useful life and observed degradation of an EV battery.

The chart posted above from this site is interesting but paints an unrealistic picture for how EV batteries are used in the real world, insofar as the test was conducted at a fixed charge and discharge rate of 1C. Unless you are DC fast charging all the time, you're charging the cells at MUCH less than 1C (~0.15C is the fastest any Tesla will charge these days on a 48 amp L2 charger), and discharge varies widely from ~6C in a performance car under full acceleration to ~0.25C in a car cruising along on the highway. How does charge/discharge rate affect capacity retention over time, and how large is the effect compared to depth of discharge or percentage of max capacity? Hard to say, but whatever the data, it's not represented in that chart.

Anyway. I've said my piece. OP sure got more than they bargained for with this thread. ;)
 
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