Honestly, I really wouldn't care about my cars battery health and all this stuff except, that Tesla's are so expensive and I want mine to last a long as possible. This car was the most expensive vehicle I've ever purchased and almost cancelled my reservation several times after making it back in 2016.
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Ready to Depart but 40 Minutes Early
- Thread starter PianoAl
- Start date
I hope this is not coming off as rude. That is so different from all I read, do you have a link or more info that a low SOC isn't bad on lithium batteries? Thanks.
Not ‘rude’ at all.
The 20% is a forum rumor. All research and the research reports that comes from the research tell us a very clear picture:
Low SOC is not dangerous. It is even the best when it comes to keeping the degradation low.
The best thing to learn might be that you self google for “calendar aging” and read the research reports, not articles about this from reporters that do not really know. Reading research reports you found might feel more safe than if I supply the links.
Anyway, here is a few links:
Link 1
Link 2
Link 3
Here is a link from Tesla. Old article, from 2006. They say that 2% or lower SOC increase the stress, and that the car shut down before reaching the SOC wiyh increased stress:
A Bit About Batteries
That article is from 2006 and all research from 2010 and later show that 0% is safe for lithium ion batteries.
0% is not completely empty. The definition of 0% is the minimum discharge level set by the battery manufacturer. This is 2.5V cell voltage for the most lithium ion batteries.
The battery manufacturer has set 4.20V as max voltage = 100% and 2.50V as minimum voltage during discharge ( = 0%).
The cell manufacturer would not set a minimum discharge level that is bad for the battery.
There is research about overdischarge (going below minimum discharge voltage) and in general the discharge need to be to a very low voltage level to create damage.
This is a chart over calendar aging for panasonic NCA ( = Tesla long range batteries):
Calendar aging wise, 0% is the SOC causing the least calendar aging.
For cyclic aging, a picture from link 3:
Looking thorough into this picture will show us that cyclic aging is least at very low SOC like cycles between 0-10% and 10-20% SOC.
Low but >0% state-of-charge per se is not bad for the battery. But don't park it unplugged for enough time that it could vampire drain below 0%.
Low state of charge may also give range anxiety to the driver.
Not really only a forum rumor. I've talked to a lot of people that deal with Lithium Ion batteries for drones and remote control cars and they all say the same thing, not to leave the battery at 100% unless it's going to be used right away and don't go lower than 10-20%. So I'm still kind of having issues believing none of that really matters. I'd think if it didn't effect the battery health all that much, it would be front page news from Tesla and every other EV manufacturer, as they wouldn't have to be concerned about a battery pack failure within the warranty, so they'd tell their customers to charge to whatever they want and not think about it.
Think I need to research this a bit more from many more reputable sources.
For a drone, you do not want to go down to zero and see the drone fall out of the sky and crash.
For other devices, it may depend on how good the BMS is in shutting down the device when it gets to 0% to avoid damage from going below 0%.
I was talking more about their charging practices, to keep their battery in good health and last a long time, so they know something about Lithium Ion battery characteristics. Those people also own Tesla's.
But it's hard to believe anymore. I sure can't wait until battery technology changes and we don't have worry about any of this stuff.
stopcrazypp
Well-Known Member
The belief it is bad to have the battery below 20% is a long running myth that has zero empirical data to support it nor any suggested mechanism for it to happen (while for high SOCs it has been demonstrated as linked above and it's well understood the chemistry behind it).
I remember discussing this years ago when someone brought up the 20% and I dug it up. The points still apply today:
In most consumer devices (and even the original Roadster), their BMS is not advanced enough to prevent overdischarge completely. Which means at low SOCs, you may overdischarge the battery, which can damage it. Nor is there typically any thermal control (a battery at low SOC at a certain temperature can easily become overdischarged when at a lower temperature). This isn't a concern in modern Teslas or EVs.
If you are running it below 20% in consumer devices, it also typically means you have a proportionally larger DOD (depth of discharge) which means lower life. This is because most consumer devices always charges to 100% (no way to set it to stop earlier), so the lower you run your battery, the larger the DOD. The worse battery degradation is from the larger DOD, it's not from the lower SOC.
For example, using the same 80% DOD, a battery that is run at 0% - 80% will degrade less than one that is run at 20% - 100%, even though the DOD is the same and in the former case you are running the battery at 20% or lower more of the time.
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Yes it is forum rumors but not limited to this forum.
Did you read the link from Tesla about batteries?
I started with lithium battery powered remote controlled models 2006, still have a lot of them (drones, RC-helicopters etc.)
In general the usage differ, a lot.
Lithium batteries have higher internal resistance at SOC’s below 20%. This means they have to flight hard to deliver high power below 20%. An RC helicopter will have very high power demands an the battery will struggle to deliver the needed power ( >10C) below 20%. This cause excessive heat and wear on the battery.
Our Tesla is different and a normal drive is using about 0.25C or so (from full to empty in 4 hours). This do not put any strain on the battery.
All research show that this is safe and even cause less wear at low SOC.
If you try to overload the battery, the Tesla limits the power to safe levels for the battery.
For the 100% SOC “issue” I havent heard the same down to the our panic as in the Tesla communities.
All data I use comes from research reports.
It quite easy to see that the calendar aging do not increase extremely above 90%.
For normal temperatures 70-100% is about the same. Leaving the car at 100% cause about the same trouble as 80 or 90%.
This is cutouts from research reports:
Most research implies that in some cases 100% causing even less calendar aging than 80-90%:
What is really clear is that a day or two doesnt brake the battery.
High SOC cause the internal resistance to increase more, 100% cause slightly higher increase over a long period than 80%.
For a day or so, we can not measure the difference.
Exactly!
Actually, more or less any research that tested this found that if the increased (or extra) DoD is very low in SOC, it do only a marginal affect to battery life.
Look at #14 and #16 at this picture (cutout from the picture in my earlier post):
#14 is 2C charge/discharge between 80-90% SOC.
#16 is 2C charge/discharge between 0-90%.
Not a very big difference concidering 80-90% is only a 10% Depth of Discharge while 0-90% is nine times(9x) the Depth of Discharge and includes the 0-20% ”very dangerous” SOC range.
If 0-20% was bad for the battery 0-90% would not manage the same number of FCE cycles before it lost 10% (yellow band) and even more FCE cycles to 85%.
Green > 95% capacity
Yellow > 90% capacity
Brown > 85% capacity
Red > 80% capacity
In a deep or large cycle, it is not the lower part of the capacity that causes the wear, it is the high SOC part that cause this.
Charging is always completed before the departure time. I kept track of it for a month and found that it's done 30 minutes prior to the departure time on average. Sometimes it's complete up to an hour ahead of time.
It rarely matters that much unless you are charging to 100% and want to know exactly when it will be done so that the car doesn't sit at 100% for a minute longer than necessary. But I wonder what the thinking was. The car could of course alter the current so that it's complete right at the desired time. I guess the engineers decided to add a margin of error, and then just do all the charging as fast as possible.
I think I would have set it up to always be done right at the departure time.
It rarely matters that much unless you are charging to 100% and want to know exactly when it will be done so that the car doesn't sit at 100% for a minute longer than necessary. But I wonder what the thinking was. The car could of course alter the current so that it's complete right at the desired time. I guess the engineers decided to add a margin of error, and then just do all the charging as fast as possible.
I think I would have set it up to always be done right at the departure time.
johnny_cakes
Member
Mine always finishes about 30 minutes to an hour before departure time (or off-peak end time). One time it actually paused for 30 minutes part way. I think it was because it was charging too quickly, but I'm not sure. This is the only time I experienced that, and the SoC graph for that night looked like this:
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