The usual Battery Degradation Topic

[AAKEE]

Long-time board troll, first post ever.

Considering that this is just the BMS projection everyone is calibrating... is it really worth the risk overcharging/discharging the battery and letting it sit in that state? Musk/Tesla have mentioned that charging above 90%, without using it immediately thereafter or letting the battery sit below 20% for an extended period... are not very good for the battery.

I'd say just drive the car and let the BMS do it's job. If it loses track of the overall range because you only use 20-30 miles a day, then at least you can rest assured that the total battery range is being under-sold. If you are really worried about the projected range.... a safer approach would be to plan a long day trip and charge it to 100% to use immediately afterwards.... then use up as much battery as possible and charge it back to your daily limit (70-90%).

It is important to remember that there are thousands of cells managed by the BMS. So, as long as you keep the State-of-Charge in that happy range, severe degradation should not be an issue. I've seen a few posts on the forum that try to reference the charge/discharge battery cycle, but it's important not to try and over-simplify from that perspective... the Tesla battery pack is not a single battery cell.

Would you please link to the Musk statement?

First of all, Teslas advice do not offer the lowest degradation. Teslas advice is supposed to be easy to follow and to reduce the risk if being stranded with a empty battery.

The 90% advice is probably a question of keeping the cycles smaller, which increases the number of cycles that can be used before the degradation is too high.

Panasonic NCA cells do not perform that well is used 100-0%. They might hold about 750 full cycles or so, before the cyclic aging causes too much wear.

On top of this, calendar aging is the dominant degradation type for most owners. Calendar aging accounts for about 3-10% the first year and cyclic aging only about a couple of percent or less during the same time.

The lower the SOC, the lower the calendar aging which can be seen in this pucture from a research report:

Theres a common miss-conception that the battery get hurt from staying below 20%.
If running completely out of juice, so the car shut down(to protect the big lithium battery), the 12V lead acid battery do not get charged and will in the end reach low SOC. This is bad for lead acid batteries, so that small 12V battery can get damaged.
The big lithium battery will not.

The bolded part in your text is not really true, at least not if understand it correct that you refer to 70-90% as the happy range.

Theres a lot of reserach that shows that the worst calendar aging happens around 70-90% SOC.

My M3P is 16 months since I got it, 37.000km/23.000mi and I still see full range(507km) at full charge.
The nominal full pack is 80.5kWh, about the same number as most M3P ’21 have as new.
I stay low in SOC and use small cycles for daily driving. Charge to 55%, drive 100km daily so 15-30% overnight and charge just before next trip to work.

 

[pipestem]

I’m in the trust the BMS group. They get paid and have access to great math and optimization tools. I should not need to overmanage. I write ML automation code - not for cars - to make users life easier.

Why not 55% overnight? I have gotten that midnight I need help call. I’d rather be sure I have the range.

I just wish Tesla was more transparent about it. The only quote I have is Musk’s “a happy Tesla is a connected Tesla”.

 

[blkswn]

I believe this was posted here before somewhere, but everyone needs to watch this to understand how degradation works.

 

[pacman3000]

Would you please link to the Musk statement?

First of all, Teslas advice do not offer the lowest degradation. Teslas advice is supposed to be easy to follow and to reduce the risk if being stranded with a empty battery.

The 90% advice is probably a question of keeping the cycles smaller, which increases the number of cycles that can be used before the degradation is too high.

Panasonic NCA cells do not perform that well is used 100-0%. They might hold about 750 full cycles or so, before the cyclic aging causes too much wear.

On top of this, calendar aging is the dominant degradation type for most owners. Calendar aging accounts for about 3-10% the first year and cyclic aging only about a couple of percent or less during the same time.

The lower the SOC, the lower the calendar aging which can be seen in this pucture from a research report:

View attachment 791111
Theres a common miss-conception that the battery get hurt from staying below 20%.
If running completely out of juice, so the car shut down(to protect the big lithium battery), the 12V lead acid battery do not get charged and will in the end reach low SOC. This is bad for lead acid batteries, so that small 12V battery can get damaged.
The big lithium battery will not.

The bolded part in your text is not really true, at least not if understand it correct that you refer to 70-90% as the happy range.

Theres a lot of reserach that shows that the worst calendar aging happens around 70-90% SOC.

View attachment 791119

My M3P is 16 months since I got it, 37.000km/23.000mi and I still see full range(507km) at full charge.
The nominal full pack is 80.5kWh, about the same number as most M3P ’21 have as new.
I stay low in SOC and use small cycles for daily driving. Charge to 55%, drive 100km daily so 15-30% overnight and charge just before next trip to work.

Sorry, when I was referring to the “happy range” it was for the 20-80% from what I have read. Ideally, keeping the state of charge close to 50% and away from either extreme… seems to be the key for keeping the battery healthy.

But for those that use a lower daily max charge and drive less often, there is a chance that the BMS may calibrate and misrepresent the total possible range. There is nothing wrong with the battery in this situation.

As far as Elon’s recommendations… he has made a few twitter posts on what he thinks the ideal range is…

https://twitter.com/x/status/448466037441179649

There was a more recent post where he did mention 90%, but I cannot seem to find it right now.

 

[AAKEE]

I’m in the trust the BMS group. They get paid and have access to great math and optimization tools. I should not need to overmanage. I write ML automation code - not for cars - to make users life easier.

I do not really understand what you are saying.
No one (not even the BMS software guys) can change the laws of physics or how the batteries wear from cycles or time.

There is no need for overmanagement.
Just follow Teslas very few advices, and you will be fine.
But this is not the same thing as having the lowest degradation possible.
In fact, using 80 to 90% can cause quite high degradation if you live in a hot climate.
Most, or probably more or less all people will not go above 30% degradation during the warranty period. But 20-25% loss after 8 years still makes a LR to a Standard range car.
So its up to everyone to choose how to do.
I do not think everyone should follow the *absolute minimum degradation way*
But I see people promoting *the best for the battery tip* that is completely wrong. There is a lot of miss-conceptions and even many people that say that Tesla says tgat going below 20% is dangerous. Tesla do not say this.

Why not 55% overnight? I have gotten that midnight I need help call. I’d rather be sure I have the range.

I just wish Tesla was more transparent about it. The only quote I have is Musk’s “a happy Tesla is a connected Tesla”.

About 49% of the people think 90% is the sweet spot for battery life. Another 49% is very sure that 50% is the sweet spot.
Only 2% of the people or so know that the two ideas above is not correct.

Tesla like us owners to have an easy life as Tesla owners. Very few advice make it easy to own a Tesla.
They do not think Tesla owners should need to be battery engineers.

If Tesla did write in the manual, or give the advise, to keep the SOC as low as possible and to stay below 55% when the car sleeps the probably would get sued by owners because the car can not go 300 miles on 50% charge.

55% overnight is okey, as it is on the better side of the steep step between 55-60% SOC, but still 40 or 30 pr 20 or 10% is better than 55%.
My car comes home with some 15-30% SOC depending on the season, and because the calendar aging is lower the lower SOC the battery has the best thing is to not charge until before the next drive.
I set the charging schedule to commence 0330 or so, so tge charge is complete in time before the next trip to work.
During weekends it still charges at the same time and driving is often much less or not at all, so it might stand at 55% during the weekend. I do this for convenience. The lowest degradation would be to leave it at low SOC and charge before next drive, perhaps monday morning.
But as 55% is on the ‘fine side’ of the curve, its still okey.

“Always connected” : minimizes the risk to get stranded, and it keeps the cycles
Smaller which is a good thing.
That single advice is supposed to fit everyone, even people that almost never use the car.

I think Teslas few advice is good.
They make the EV owning easy.
(But it will not minimize the degradation)

 

[AAKEE]

Sorry, when I was referring to the “happy range” it was for the 20-80% from what I have read. Ideally, keeping the state of charge close to 50% and away from either extreme… seems to be the key for keeping the battery healthy.

But for those that use a lower daily max charge and drive less often, there is a chance that the BMS may calibrate and misrepresent the total possible range. There is nothing wrong with the battery in this situation.

We ( I and the researchers that have done intense testing of lithium batteries) know that the lower SOC, the better. Theres really no doubt about this.
80% might be the worst SOC to use for the calendar aging according to some research and most other research reports show signs of this as well.

The BMS can get off track sometimes, but in most cases not by far. Using the BMS calibration trick might increase the on-screen range and the BMS calculated battery capacity but in many cases the BMS reverts to the same values after a while.
BMS calibration is in many cases a way of pleasing the owner but actually it imduce increased wear instead(not by much, but in principle it do).
For me, charging to 55% and using some 25-35 each day, my BMS get off track but it do not show to low capacity, instead it overestimate the capacity. I probably have lost about 2.5% by now, so 79.5kWh (out of 82) is probably the real capacity but my BMS say about 80.5-81kWh.

The lower the SOC, the lower the calendar aging is. Period.
This means that going below 20% do not cause any extra strain on the battery.

The lower the SOC is, the lower the cyclic aging. From one research report, using NCA cells, we saw that the cyclic aging caused a 10% drop of capacity when doing 600EFC cycles around 70% ( between 75-65%) This is about the same as 180K km or 120K miles for an Long range model 3.
But the same number of cycles around 30%( = 35-25% cycles) only degraded the battery 2%.

We also know that smaller cycles are causing much less degradation than bigger cycles, so charge often( “always connected”) is good.

Summarized:
-The lower the SOC, the better.
-Charging shortly before the drive means lowering the average SOC and reduced calendar aging.
-Charge often( ie, every night), keeps the cycles small.

I do not mean that everyone need to follow this. The reason for me to writing this twice a week here on TMC is not to persuade everyone to change the behavoiur.
I do this because there are some wide spread myths about what’s best for the batteries.

The standard post is:
”I already have 15% degradation. This despite the fact that I baby the battery and always charge to 80% I am very unhappy.”

I try to kill the myths. The standard phrase above is mostly because the myths tell people the wrong thing.
Understanding a few facts about battery degradation probably make people to be less unhappy, like “I know leaving the car at 80% will degrade the battery, specially in my hot climate. But I need to use 80% and I can not use the charge just in time technique so it will happen and I know why”

As far as Elon’s recommendations… he has made a few twitter posts on what he thinks the ideal range is…

There was a more recent post where he did mention 90%, but I cannot seem to find it right now.

Elon answer a question about the best choice of two, 90-40% or 80-30%.
Elon’s answer is correct. 80-30% is better than 90-40, but he do not say that 80-30 cause the lowest degradation of all possible , and he do not say that below 30% is bad for the battery.
So from my point of view Elpns answer is not the ”ideal choise”.

 

[AAKEE]

There was a more recent post where he did mention 90%, but I cannot seem to find it right now.

I have seen references to “you will be fine with 90%” from Elon Musk.

Thats true.

But it will not be the lowest degradation.

Musk do not talk about having the battery live forever.

Tesla do not want us to be engineers.
Very few easy advices makes the life easy for us.
Tesla aim to show the world that using electric vehicles do not mean a lot of compromise’s.
A 100 page book about batteries, “Don’t do this” and “Not allowed to do that” wont help in this case.
Tesla will tell us as little as possible and they will keep the advice/rules as few and open as possible.
They of course know about battery aging, but they think only Tesla need to know the whole part and the car owners do not.
The battery will in most cases survive the car anyway, so there is no need to babysit the battery.

 

[pacman3000]

I have seen references to “you will be fine with 90%” from Elon Musk.

Thats true.

But it will not be the lowest degradation.

Musk do not talk about having the battery live forever.

Tesla do not want us to be engineers.
Very few easy advices makes the life easy for us.
Tesla aim to show the world that using electric vehicles do not mean a lot of compromise’s.
A 100 page book about batteries, “Don’t do this” and “Not allowed to do that” wont help in this case.
Tesla will tell us as little as possible and they will keep the advice/rules as few and open as possible.
They of course know about battery aging, but they think only Tesla need to know the whole part and the car owners do not.
The battery will in most cases survive the car anyway, so there is no need to babysit the battery.

We ( I and the researchers that have done intense testing of lithium batteries) know that the lower SOC, the better. Theres really no doubt about this.
80% might be the worst SOC to use for the calendar aging according to some research and most other research reports show signs of this as well.

The BMS can get off track sometimes, but in most cases not by far. Using the BMS calibration trick might increase the on-screen range and the BMS calculated battery capacity but in many cases the BMS reverts to the same values after a while.
BMS calibration is in many cases a way of pleasing the owner but actually it imduce increased wear instead(not by much, but in principle it do).
For me, charging to 55% and using some 25-35 each day, my BMS get off track but it do not show to low capacity, instead it overestimate the capacity. I probably have lost about 2.5% by now, so 79.5kWh (out of 82) is probably the real capacity but my BMS say about 80.5-81kWh.

The lower the SOC, the lower the calendar aging is. Period.
This means that going below 20% do not cause any extra strain on the battery.

The lower the SOC is, the lower the cyclic aging. From one research report, using NCA cells, we saw that the cyclic aging caused a 10% drop of capacity when doing 600EFC cycles around 70% ( between 75-65%) This is about the same as 180K km or 120K miles for an Long range model 3.
But the same number of cycles around 30%( = 35-25% cycles) only degraded the battery 2%.

We also know that smaller cycles are causing much less degradation than bigger cycles, so charge often( “always connected”) is good.

Summarized:
-The lower the SOC, the better.
-Charging shortly before the drive means lowering the average SOC and reduced calendar aging.
-Charge often( ie, every night), keeps the cycles small.

I do not mean that everyone need to follow this. The reason for me to writing this twice a week here on TMC is not to persuade everyone to change the behavoiur.
I do this because there are some wide spread myths about what’s best for the batteries.

The standard post is:
”I already have 15% degradation. This despite the fact that I baby the battery and always charge to 80% I am very unhappy.”

I try to kill the myths. The standard phrase above is mostly because the myths tell people the wrong thing.
Understanding a few facts about battery degradation probably make people to be less unhappy, like “I know leaving the car at 80% will degrade the battery, specially in my hot climate. But I need to use 80% and I can not use the charge just in time technique so it will happen and I know why”





Elon answer a question about the best choice of two, 90-40% or 80-30%.
Elon’s answer is correct. 80-30% is better than 90-40, but he do not say that 80-30 cause the lowest degradation of all possible , and he do not say that below 30% is bad for the battery.
So from my point of view Elpns answer is not the ”ideal choise”.

I completely understand and agree about your comment on the myths and misinformation floating around. I had a hard enough time finding any actual explanation on why the Tesla's 90kWh battery packs exhibited higher than normal degradation back when I was shopping for a Tesla. I think the concept of battery degradation will become more important, but it will evolve as the chemical composition changes (as with the LFP batteries). I'll never claim to be a subject matter expert, because I know this field will be evolving and I'm open to learning. What is important to note is that what works now, may not work in the future.

While it may be true that a lower SoC on a single physical lithium cell battery may be the best way to avoid battery degradation for storage.., those charts you are using may be adding to the confusion. What would be even more interesting is the data beyond the 12-month mark, does the degradation stabilize? I'm going to disagree with the notion that it's healthier to use a lower state of charge on a Tesla, because you have to remember that the BMS is managing it. Who knows how the cells are charged across the board? Just because a driver sees 20% on their available battery, does not represent that all 6000+ cells are charged at 20% across the board. I feel that Tesla's BMS is being over-simplified in a lot of these discussions.

Once a Tesla drops below a certain percentage, certain functions turn off to preserve available battery. For a performance version, the total output is noticeably affected anytime you go below 50%. A good segue here would be a comparison to smartphones: While it's true that a lower charge on a smartphone may be good to preserve the battery capacity over time, the phone is useless and will be irrelevant in a few years. So what was the point in extending the life of that battery by a few percentage to use a phone that is practically in 'safe-mode'?

You did touch on something in one of your replies which I agree with whole-heartedly though:
It's just something I've adopted and don't plan to change. My suggestion is to keep the depth of discharge and battery cycle small.
Let the battery management do it's thing. Charge often-- remember that regen is kind of doing some of this already while we are driving.

 

[pacman3000]

I have seen references to “you will be fine with 90%” from Elon Musk.

Thats true.

But it will not be the lowest degradation.

Musk do not talk about having the battery live forever.

Tesla do not want us to be engineers.
Very few easy advices makes the life easy for us.
Tesla aim to show the world that using electric vehicles do not mean a lot of compromise’s.
A 100 page book about batteries, “Don’t do this” and “Not allowed to do that” wont help in this case.
Tesla will tell us as little as possible and they will keep the advice/rules as few and open as possible.
They of course know about battery aging, but they think only Tesla need to know the whole part and the car owners do not.
The battery will in most cases survive the car anyway, so there is no need to babysit the battery.

View attachment 791292

Sorry, I thought this whole post was a copy/paste. LOL.

I agree 100%:
The battery will in most cases survive the car anyway, so there is no need to babysit the battery.

 

[AAKEE]

While it may be true that a lower SoC on a single physical lithium cell battery may be the best way to avoid battery degradation for storage.., those charts you are using may be adding to the confusion. What would be even more interesting is the data beyond the 12-month mark, does the degradation stabilize?

Most, if not all researchers agree to that calendar aging reduce with the square root of time. If you have 5% calendar aging the first year, youre at 7% after two years and some 8.5 after three years and 10% after four years.

I'm going to disagree with the notion that it's healthier to use a lower state of charge on a Tesla, because you have to remember that the BMS is managing it. Who knows how the cells are charged across the board?

The BMS can not do wonders. The same physics that apply to a single cell during *time* applies to a bunch of cells in a pack as well.
We that use Scan My Tesla know exactly whats going on in a pack and we can se the voltage in each brick of 46 cells.(M3LR/P has 4416 cells in the pack).
SOC Is determined by the voltage in the pack/cells. 4.20V is 100% SOC and 0% om the screen is some 4.5% true SOC. The buffer is the part below 0% on the screen.
The battery pack strives to keep the cell voltage as even as possible, and I have 4mV more or less anytime not driving around.

Just because a driver sees 20% on their available battery, does not represent that all 6000+ cells are charged at 20% across the board. I feel that Tesla's BMS is being over-simplified in a lot of these discussions.

Once a Tesla drops below a certain percentage, certain functions turn off to preserve available battery. For a performance version, the total output is noticeably affected anytime you go below 50%

The reason for the power drop is that the internal resistance increases and the cell voltage drop, making full power impossible.
Tesla mostly do not limit the power, so the reduced power comes from the battery not being anle to deliver power. All of this can be seen clearly with scan my tesla.

So what was the point in extending the life of that battery by a few percentage to use a phone that is practically in 'safe-mode'?

Thats right!

Precisely what I say as well. My goal is to kill some of the myths about batteries and degradation.
It is up to everyone to choose the tactics.

There is a lot of posts though, with people that is not happy about the degradation, and as I wrote before the most common is ”my battery already have lost XX % and I babt the battery at 80%”

These persons have the right to find out how the battery degradation really work, and to know that the usual myths is not true.

 

[Bouba]

I have a question that is causing me some confusion....there has been some controversy over Tesla not reaching its EPA rating (unlike most other electric car brands) in response Tesla has said that you have to drive the car till it is completely empty to reach the EPA rating...ie...below zero
The EPA is on the screen....so if this is 100% to 0% range, where is this buffer?

 

[AAKEE]

I have a question that is causing me some confusion....there has been some controversy over Tesla not reaching its EPA rating (unlike most other electric car brands) in response Tesla has said that you have to drive the car till it is completely empty to reach the EPA rating...ie...below zero
The EPA is on the screen....so if this is 100% to 0% range, where is this buffer?

The screen use the EPA figure, and yes, you need to drive the car until it stop. Thats about 4.5% below zero.
The screen hides the 4.5% during the SOC getting lower, thats it.
So, using the consumption of the EPA trdt you need to drive ubtil the car stops.
If you just drive until 0%, you’re 4.5% short on the range.

The 4.5% below zero on the screen is the buffer. You can use it.

 

[Bouba]

The screen hides the 4.5% during the SOC getting lower, thats it.

AAKEE, the line above...are you saying....at 100% charge the 0% represent true zero (ie the car stops) but as you drive and the SOC goes down, it moves the 0% so that now it contains a buffer (ie minus 4.5%) ?
I hope I’m not misinterpreting you

 

[AAKEE]

AAKEE, the line above...are you saying....at 100% charge the 0% represent true zero (ie the car stops) but as you drive and the SOC goes down, it moves the 0% so that now it contains a buffer (ie minus 4.5%) ?
I hope I’m not misinterpreting you

We go over it once again. English is not my native.

100% is true 100%.

0% on the screen hides 4.5% of the capacity below the 0% screen SOC.

At 100% charge, in the LR and P the cell voltage is 4.20V. This means that there is no buffer or margins there.

At 100% with a new battery, which the BMS thinks have full capacity, you can read the EPA range on the screen.
If you drive with the EPA consumption until the cars stops you will have driven the EPA range. The reason that it works like this is the EPA regulation(Range test means driving until the car stops).

The minimum voltage is 2.5 V/cell for these batteries. Tesla also list the min and max voltage in the BMS and max is 4.20V/cell and min 2.5 V/cell. In the BMS max is 403 V for the pack, which is 4.20V/cell.

I have been down to -2% SOC, average cell voltage 2.84V at that time. The voltage curve is very steep below 3V so it is probable that the shut down voltage is close to 2.5V.

The 0% on the screen is when the battery still have 4.5% energy left, the cell voltage is about 3.1V, or slightly above.

This means that the SOC percentage on the screen will show a lower SOC than the “true SOC”.
True SOC is divided from 100 to 0% between 4.20 to 2.50 V/cell.

 

[Bouba]

We go over it once again. English is not my native.

100% is true 100%.

0% on the screen hides 4.5% of the capacity below the 0% screen SOC.

At 100% charge, in the LR and P the cell voltage is 4.20V. This means that there is no buffer or margins there.

At 100% with a new battery, which the BMS thinks have full capacity, you can read the EPA range on the screen.
If you drive with the EPA consumption until the cars stops you will have driven the EPA range. The reason that it works like this is the EPA regulation(Range test means driving until the car stops).

The minimum voltage is 2.5 V/cell for these batteries. Tesla also list the min and max voltage in the BMS and max is 4.20V/cell and min 2.5 V/cell. In the BMS max is 403 V for the pack, which is 4.20V/cell.

I have been down to -2% SOC, average cell voltage 2.84V at that time. The voltage curve is very steep below 3V so it is probable that the shut down voltage is close to 2.5V.

The 0% on the screen is when the battery still have 4.5% energy left, the cell voltage is about 3.1V, or slightly above.

This means that the SOC percentage on the screen will show a lower SOC than the “true SOC”.
True SOC is divided from 100 to 0% between 4.20 to 2.50 V/cell.

AAKEE, thank you for that I am sorry for testing your linguistic skills too much (by the way your English is excellent!). You are the best resource on the internet.....but I will try not to wear you out

 

[inigoml]

View attachment 778271

No Aakee.

Do you have the link to this paper? It's really interesting what you posted here and I would like to read the full paper. For NCA I got it, but not this comparative that for me is really cool.

As always your posts are pure gold!

Thank you!

 

[AAKEE]

Do you have the link to this paper?

ShieldSquare Captcha

I recommend this report also, it covers most things, also explained better for a novice or non battery experts

https://mediatum.ub.tum.de/doc/1355829/document.pdf

 

[inigoml]

ShieldSquare Captcha

I recommend this report also, it covers most things, also explained better for a novice or non battery experts

https://mediatum.ub.tum.de/doc/1355829/document.pdf

Thank you, mate.
Second one is my Bible since I got an M3P (NCA based). ;-)

 

[gtg465x]

We ( I and the researchers that have done intense testing of lithium batteries) know that the lower SOC, the better. Theres really no doubt about this.
80% might be the worst SOC to use for the calendar aging according to some research and most other research reports show signs of this as well.

The BMS can get off track sometimes, but in most cases not by far. Using the BMS calibration trick might increase the on-screen range and the BMS calculated battery capacity but in many cases the BMS reverts to the same values after a while.
BMS calibration is in many cases a way of pleasing the owner but actually it imduce increased wear instead(not by much, but in principle it do).
For me, charging to 55% and using some 25-35 each day, my BMS get off track but it do not show to low capacity, instead it overestimate the capacity. I probably have lost about 2.5% by now, so 79.5kWh (out of 82) is probably the real capacity but my BMS say about 80.5-81kWh.

The lower the SOC, the lower the calendar aging is. Period.
This means that going below 20% do not cause any extra strain on the battery.

The lower the SOC is, the lower the cyclic aging. From one research report, using NCA cells, we saw that the cyclic aging caused a 10% drop of capacity when doing 600EFC cycles around 70% ( between 75-65%) This is about the same as 180K km or 120K miles for an Long range model 3.
But the same number of cycles around 30%( = 35-25% cycles) only degraded the battery 2%.

We also know that smaller cycles are causing much less degradation than bigger cycles, so charge often( “always connected”) is good.

Summarized:
-The lower the SOC, the better.
-Charging shortly before the drive means lowering the average SOC and reduced calendar aging.
-Charge often( ie, every night), keeps the cycles small.

I do not mean that everyone need to follow this. The reason for me to writing this twice a week here on TMC is not to persuade everyone to change the behavoiur.
I do this because there are some wide spread myths about what’s best for the batteries.

The standard post is:
”I already have 15% degradation. This despite the fact that I baby the battery and always charge to 80% I am very unhappy.”

I try to kill the myths. The standard phrase above is mostly because the myths tell people the wrong thing.
Understanding a few facts about battery degradation probably make people to be less unhappy, like “I know leaving the car at 80% will degrade the battery, specially in my hot climate. But I need to use 80% and I can not use the charge just in time technique so it will happen and I know why”





Elon answer a question about the best choice of two, 90-40% or 80-30%.
Elon’s answer is correct. 80-30% is better than 90-40, but he do not say that 80-30 cause the lowest degradation of all possible , and he do not say that below 30% is bad for the battery.
So from my point of view Elpns answer is not the ”ideal choise”.

Very good advice. I wonder, have you posted your thoughts on LFP strategy? For battery degradation, I assume the same principles apply, but there is the added complexity of needing to charge to 100% sometimes to prevent BMS SOC estimates from drifting too much and becoming too inaccurate. I’m trying to figure out what would be the best balance of reducing degradation and keeping BMS calibrated well enough.

 

[AAKEE]

Very good advice. I wonder, have you posted your thoughts on LFP strategy? For battery degradation, I assume the same principles apply, but there is the added complexity of needing to charge to 100% sometimes to prevent BMS SOC estimates from drifting too much and becoming too inaccurate.

I have touched the subject sometines.
It is easy to dig a whole that make the answer not very short and also get everlobg discussions about the base for the strategy.

Charging to 100% is not very bad, even for NCA or NMC.
The forum truth is to not let the car stand long time if charged to 100%.
While it is true that letting it stand at 100% cause more calendar aging/degradation than if it stands at 30% it is not at all catastrofic. In some cases 100% is less bad than 75-85%.
When being above a plateau, the degradation is more or less the same, unless in extremely high temperatures.

As we can se, it is about the same degradation above the “step”. And yes, the calendar aging hapoens even if we use the car, and for most people it isnot used for 22hours a day. The graphs above is valid for us and our EV’s!

The above in memory, 100% is not really worse than 70-90%.
That research report has a few years but we have no data telling us that new LFP is taking a lesser hit than before. Perhaps/probably the rate is slightly slower than in the chart but the basic principle probably still is valid.

I would charge to 100% once a week, but I would have it at lower SOC the other days, 50-70% depending on the minimum SOC covering my needs.
I would charge late (finished shortly before the drive).

We have some data, but as the LFP cars have a hard time judging the true SOC below 100% I would guess that its at least slightly harder for the BMS to judge the capacity as well, as different true SOC + the difference in energy in/ out is part of the calculation.

The charts for LFP’s at teslalogger.de show us that the LFP degradation is about the same or slightly less than other teslas (NCA mainly). We know the LFPs is non sensitive to large cycles and can do many of them so the degradation we see is more or less calendar aging only.

I’m trying to figure out what would be the best balance of reducing degradation and keeping BMS calibrated well enough.

It probably is per above