All other parts in your post is correct, but not this.
There is no reason not to run the car below 20%.
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What should my ideal charge percentage be?
- Thread starter Al Sherman
- Start date
There is no reason not to run the car below 20%.
12Pack
Member
Any reason you think Tesla are deliberately providing wrong guidance on this?
From the manual:
I think you read things in that line that Tesla newer wrote.
This is a quite common part of the myths around EV’s and batteries, to fill in things in the text that is not there by yourself.
The headline is [Best charging practices].
Charging when reaching 20 or 10% is a good thing, asthe practical range is low.
It does not say that below 20% is too low either. On the other places in the manual Tesla refer to ”Too low” as 0%, and that the HV batt disconnects to protect itself and that might cause the LV Battery (12V or small lithium LV-battery) to completely discharge, which is bad for the 12V lead acid battery at least.
What we know from a lot of research* is that lithium batteries degrade mostly from time the first 5-8 years (called calendar aging) and that calendar aging is lower at lower state of charge (down to 0%).
Cyclic aging is small but in general lower at lower SOC for the current rates we use in hour cars. In a few research reports we see slightly increased cyclic aging below 20% but as cyclic aging is such a small part of the total the first ~5 years or so, the calendar aging reduces at least to the same amount as the cyclic aging increases.
There also is research using actual Tesla cells showing how the actual tesla cells behave and that the other research is valud for the actual Tesla cells as well.
So even if Tesla has marked <20% yellow and <10% red ok the battery its more to be compared with the red part of and ICE-vehicles fuel meter showing red at the lower part that means ”time to consider refuelling”.
I guess you might be one of the people thinking that leaving the car at 100% is very bad for the battery?
12Pack
Member
Indeed I am. As is borne out by the bulk of the literature, the instructions from battery manufacturers, as well as my personal experience with Li-ion batteries.I guess you might be one of the people thinking that leaving the car at 100% is very bad for the battery?
I could not find Peter Keil, the first author the 18650 batteries study you quoted at TUM, so I have reached out to the JES for the peer reviewers as I don't follow some of the controls and methodology (I am a frequent author at JES).
You blithely stated that you replicated some of the methodology that I had questioned regarding repeated measurements of the same cells and found no difference yourself. Can you attach your data please? I am genuinely curious on this topic.
Also that study only considers calendar aging of an individual cell - the result of the formation of passivation layer at the electrode/electrolyte interface, but does not consider this in conjunction with cycle degradation caused by lithium loss. In our real world we have both. So while storage at low SoC may be good for calendar aging of an individual cell, the concurrent effect of lithium aging due to cycling it back up for a usable range regularly may result in higher overall degradation. Also storage at too low of SoC could prevent the BMS from adequately rebalancing the cells in an actual battery pack.
I don't agree with your interpretation of the instructions in the manual to essentially say that Tesla only recommends not going below 20% is because that means you will run out charge soon. LoL.
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E90alex
Active Member
They never said they don’t go below 20%. They said avoid going “too low”. They never specified what “too low” is.
The comment in parenthesis about the icon turning yellow below 20% doesn’t mean 20% is “too low”, but I can see how it can be interpreted that way.
12Pack
Member
Indeed you are right - but I do interpret the advice to not run too low is because of battery aging rather than simply running out of charge. Thanks.
This thread is enlightening!
Now starting from this: "The cells age from calendar aging from [Time x SOC x Temperature]"
- Time - we can't influence this
- SOC - based on all previous posts (with graphs and so on) best is to charge to 55%
- Temperature
- while driving - we can't influence this (depending on the external conditions)
- when starting - charge late ( so the battery will be warm)
- while charging - that's where I struggle with ... how do I know the temperature the battery gets to while I am charging? If know that, I can dial up/down the charging amps to keep the battery temp low.
(NCR18650B here!)
Now starting from this: "The cells age from calendar aging from [Time x SOC x Temperature]"
- Time - we can't influence this
- SOC - based on all previous posts (with graphs and so on) best is to charge to 55%
- Temperature
- while driving - we can't influence this (depending on the external conditions)
- when starting - charge late ( so the battery will be warm)
- while charging - that's where I struggle with ... how do I know the temperature the battery gets to while I am charging? If know that, I can dial up/down the charging amps to keep the battery temp low.
(NCR18650B here!)
Please show me any litterature stating that, and also instruction from battery manufacturers stating that?
Tesla use Panasonic NCA cells in S/X and 3/Y in USA. LG M50 NMC cells is used in Europe, and seem to be comming in US as well for 3/Y.
Here’s Pansonic’s NCR18650BD and all documents that comes with it
NCR18650BD - Lithium-ion Batteries - Secondary Batteries (Rechargeable Batteries) - Panasonic
Here’s a Spec sheet:
Page 1 & 2
Page 3 & 4
Link to Peter Keil.de including contact formular
My tests is only on hand written pages. Initially I had planned to make a few pictures from my findings but they where so close to other reports testing Panasonic NCA cells, so I did not think it was worth the time to only reproduce a picture like this:
(My findings is very close to this, inclufing the slightly lower degradation at 100%.)
I took the essence of several studies for calendar aging and cyclic aging and made it into math. I used that math on my own M3P (often parked below 20%)
During the first year I initially thought my car had slightly lower degradation than my formulas, until I found that the average cell temp was lower than my prediction. The average SOC was close, but the average cell temp was 13.46C. After adjusting for that, my car was spot on the predicted line.
I continued to watch this for one year further, after that I started to test the calculations on cars in this forum and a swedish forum. The most hard value to get correct is the average cell temp which causes a slight variation but in general the calculation of the capacity (and degradation) is quite close in more or less any case.
Actually there is two cars with noticable lower degradation than the formulas. Both cars are living in a very cold environment and I deliberately toned down the reduction of very low temperatures (due to very few research reports testing this and a little split between those).
More or less any other car match the formulas quite well.
If calendar aging and cyclic aging could not be tested separately and then joined for the data, my formulas would not be able to hot that well.
(During cyclic aging tests, the cells are affected by calendar aging as well so that need to be taken into account)
There simply is no data that supports the idea that below 20% would be bad.
20% displayed SOC is about 24% true SOC, do you think it is bad to go below 24% true SOC?
About the upper end
Lilthium batteries, like NCA and NMC can be charged to 4.4V or so, but they show a quite bad cyclic life.
The 4.20V upper charge limit is chosen to give the batteries a decent cyclic number life. This has been selected so the cells that are sold work good enough and dont die too early. Most cells used for flash lights/e-cigarettes or you name it, is charged to 4.20V per cell ( = the same 100% as in our cars). More or less all manufacturers has chosen 4.20V as the 100% upper limit. Do you think they would choose a 100% upper limit that cause most cells to die premature and the customers returning with a RMA Case because of broken batteries or du you think the bransh selected a safe 100% limit?
About the lower end
All lithium batteries of these chemistries
Have e end-of-discharge voltage of 2.5V to 3.0V. (A few has 2.3 or 2.4V).
Panasonic NCA has 2.5V stated by the manufacturer and most tests do discharge to that limit. (Mostly 100-0% in the research tests). They do not break from this, they are designed to be cycled within that range.
Tesla are at about 3.1-3.2V at 0% displayed SOC.
Overdischarge do not cause issues/damage until the cells are well below the lower discharge limit. (There is research on this as well, se picture below)
Attachments
This is a spec sheet of the LG M50, used in M3/MY in Europe:
https://www.dnkpower.com/wp-content/uploads/2019/02/LG-INR21700-M50-Datasheet.pdf
One of the specs is how to check the storage characteristics.
Charge full to 100% according to the charging spec, leave the cell for 30 days at 25C +/-2C.
(This is not a degradation test but a test to see how much self discharge the battery has, or rather how much energy it can deliver after 30 days at 100%.)
There is no caviat about storing at 100% in this case either.
To get a balance to the discussion, I do not recommend storing the batteries at 100%.
Compared to storing at 55% or below for NCA (or 60% for NMC) 100% about doubles the degradation rate.
Also, the internal resistance increases faster at 100%.
Calendar aging is about as ”bad” at 80% as at 100%, in most cases only small differences.
The myth is that 100% is very bad, which it is not. In most cases 80 and 100% are about the same, and in high ambient 100% might degrade faster than 80% (specially for NMC) but it still is at rates not extremely faster than at 80%.
We do not need to drive asap after a 100% charge. If you normally charge to 80-90% there is really not a big difference.
If you normally charge to 55% you do not need to drive asap either. Each hour at 100% wear about as much as two hours at 55%.
In most cases, there is no need to leave the car at 100% for extended time so we better leave that to the few times it actually is needed.
https://www.dnkpower.com/wp-content/uploads/2019/02/LG-INR21700-M50-Datasheet.pdf
One of the specs is how to check the storage characteristics.
Charge full to 100% according to the charging spec, leave the cell for 30 days at 25C +/-2C.
(This is not a degradation test but a test to see how much self discharge the battery has, or rather how much energy it can deliver after 30 days at 100%.)
There is no caviat about storing at 100% in this case either.
To get a balance to the discussion, I do not recommend storing the batteries at 100%.
Compared to storing at 55% or below for NCA (or 60% for NMC) 100% about doubles the degradation rate.
Also, the internal resistance increases faster at 100%.
Calendar aging is about as ”bad” at 80% as at 100%, in most cases only small differences.
The myth is that 100% is very bad, which it is not. In most cases 80 and 100% are about the same, and in high ambient 100% might degrade faster than 80% (specially for NMC) but it still is at rates not extremely faster than at 80%.
We do not need to drive asap after a 100% charge. If you normally charge to 80-90% there is really not a big difference.
If you normally charge to 55% you do not need to drive asap either. Each hour at 100% wear about as much as two hours at 55%.
In most cases, there is no need to leave the car at 100% for extended time so we better leave that to the few times it actually is needed.
I would charge to 80% and not worry about it. Charge to 100% for trips when it makes sense to do so.Following your advice I keep 55% at home. The reason I got a new model was more range
Joke aside, once a while should I charge to 100%? or 80%? Or going between 10%-20% to 55% for many cycles OK?
Have an 11 year old battery charging to 90% for many years and still doing fine.
Ideal charge limit probably depends on what kind of batteries are in your Tesla. Our 2023 Model Y LR recommends charging to 80% for daily driving. The 2022 Model 3 single motor unit we have right now as a loaner recommends setting the charge limit to 100% and actually charging it fully at least once a week.
80% is not the ideal charge like that.
Even if it can be interpreted that 80% is the recommended daily charge level, that text is only shown if you put the slider above 80%.
At all other settings that information will not come up.
Before the change to 80% Tesla said ”below 90%, which included all settings from 50% to 89%.
That, plus the knowledge that calendar aging (which cause the most part of the degradation) is lower at lower SOC indicate to us that a lower setting is better than 80%.
For panasonic NCA cells, 55% displayed or below is better.
For LG NMC/NCMA 60% or lower is better.
zoomer0056
Active Member
True. However, the recommended daily charge limit is demarked on the charging screen slider as a mark between daily and trip charging. In some cases it's 90%, and since update 2023.26 the mark is at 80%.
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E90alex
Active Member
The recommended daily charge limit is a range from 50-80%. 80% is the maximum in the recommended range, that does not mean 80% is the best or that you should definitely set it to 80%. And there is data proving that 80% is indeed not the best if you’re concerned about degradation.
If you truly need 80% daily, then yes by all means charge to 80% or more as needed.
If you don’t care about degradation, then set it to whatever you want - the battery will still make it through the warranty period.
But if you are concerned about degradation and you only use 0-30% daily, there is no real need to go beyond 50% charge limit (except for LFP that needs an occasional charge to 100%)
zoomer0056
Active Member
We used to charge our leased 2021 Model 3P to 70% for daily driving because of the scale on the charge screen as noted above. Our 2023 Model Y LR, on the other hand, specifically encourages charging to 80% for daily driving. There is no range - 80% is what they recommend. Thus, we've done that so far for the month we've had the new car. 
E90alex
Active Member
Could you post a picture of that?We used to charge our leased 2021 Model 3P to 70% for daily driving because of the scale on the charge screen as noted above. Our 2023 Model Y LR, on the other hand, specifically encourages charging to 80% for daily driving. There is no range - 80% is what they recommend. Thus, we've done that so far for the month we've had the new car.
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