Favor Low SoC or Small Cycles?

[Drinyth]

Have you read the manual for your car? What did it say?

General recommendation from Tesla or Elon, charge to 80 or 90% unless you need to go on a trip, which in that case you can charge to 100%.

Tesla built the battery to take a beating.

ALL of the studies and recommendations that you hear are from studies about other batteries, not the specific formulations that Tesla uses. The formulation makes a huge difference.

For a newer car, your batteries are designed to last over 300,000 miles.

Enjoy the car, charge as fits your lifestyle and needs. One of the few statements from Tesla, a plugged in car is a happy car.

By charging your car to only 50% you are effectively throwing half of your range away. You bought it, you paid for it, so use it!!!

Your car will lose a percentage over the first year or so, this is expected and completely normal. This occurs no matter how you charge it.

Ask the folks who recommend 50% how much range are they expecting to add to the battery. Is it a year? a month? or a mile. No one really knows.

I have read the manual and the FAQ. The manual doesn't really specify values and only says to charge to "the level of charging you want". The FAQ is a little more clear in that it says to charge "within the 'Daily' range bracket, up to approximately 90%". That still doesn't clarify how 50% is different from 90%. As E90alex stated, if 90% is the preferred value, why not just make everyone charge to 90% and not give people an option?

I've seen Elon's suggestion to charge to 80-90%. I've also seen him saying that Jeff Dahn's suggestion of 70% being better than 80-90% was correct (

https://twitter.com/x/status/1068921251832492035

), but he still says 80% is preferable to him for convenience.

If my daily needs warranted me needing 80% of a charge to comfortably get me through a day, I'd charge it to 80%. But 50% is more than enough to get me through a day of typical driving. On a day when I'm going to take a long trip, I'll charge it up to 100% without a second thought. But, assuming there is battery longevity gains at lower SoCs (however small they might be), why charge above 50% on a daily basis when my total daily mileage is a small fraction of what that 50% provides?

As for how much range one can expect to gain from the battery by keeping it at 50% vs 80-90%? That's the million dollar question. Tesla promises no more than 30% degradation over its warranty period. Honestly, that sounds like quite a lot. If keeping it at 50% is only going to make a 1% difference over 10 years, perhaps it's not worth even talking about it. But if it keeps the capacity at 5-10+% by the time the warranty expires, I put a decent amount of value in that. Especially for those of us that plan on keeping the car past its warranty period.

I appreciate the discussion from everyone - those who are in the 90% camp and those who are in the 50% camp. I think everyone here agrees to charge to a level that meets your daily needs and to never sacrifice convenience in an effort to preserve battery capacity. But daily needs and convenience are two variables that can be drastically different from one person to the next. Hence I fully agree with you - "Enjoy the car, charge as fits your lifestyle and needs."

 

[AAKEE]

Turns out this is a highly debatable statement.

Nope. I’ll tell you why below.

On the surface of it small cycles seem better than larger ones, but you need many more small cycles to match one large one. For example, you will need five 10% cycles to match a single 50% cycle.

This statement is because you lack knowledge about how these things is tested and evaluated. We will sort this out further down

Any descent chart or graph use Full Cycles Equivalent (FCE) to compare different cycle tests.

One FCE is the same energy as a full 100% to 0% cycle.
This means for 50% DoD cycles, two is needed to cover one FCE.
For 10% DoD cycles, ten is needed to cover one FCE.

The left 100-0% cycle, covered about 650 cycles before reaching the 20% branch standard with 0.5A current. Each of these cycles is one FCE, thus 650 FCE.

The right graph with about 80% (4.0V) to 0% cycles covered about 1250 cycles of 80-0%. Thats the double amount of simple cycles compared to the 100-0%.

These 80 to 0% only covered 80% of the 100-0% cycles so these are presented as FCE’s instead. 1250 x 0.8 = 1000 FCE.

FCE is used as it directly show the degradation per energy delivered from the battery. In a EV cases rhis relates directly to the degradation per mile and how many miles the battery will hold up.

In some cases there is still a need or wish to count single cycles, this chart shows ”simple cycles only so we need to count energy to evaluate the energy thougput ir the miles it holds in an EV.
100% DoD = 300cycles-300FCE.
80% DoD = 450 cycles - 360 FCE.
50% DoD= 1000 cycles - 500 FCE.
20% DoD = 3000 cycles - 600 FCE.
(This charts lacks information aboyt where the cycles are placed. We know from research that the lower the cycle is placed, the lower the degradation. Small cycles at low SOC often make the batteries able to handle a very high number of FCE)

Source:
https://www.researchgate.net/public...attery-Lifespan.pdf?origin=publication_detail

The chart below is very useful about DoD and where the cycles are placed.
There is different tempersture intervalls shown to the right, so comparing should mainly be at the same tempersture.
Also each tested cycle is labeled with different ”C”, comparing should be done with the same C.
C = the current (Amps) load, higher number is a higher load.

 

[AAKEE]

Have you read the manual for your car? What did it say?

I recommend that every EV owner read the manual and find what Tesla actually says.
Most of the ”Tesla says” is forum rumors.

General recommendation from Tesla or Elon, charge to 80 or 90% unless you need to go on a trip, which in that case you can charge to 100%.

What you refer to is someone asking Elon ”Should I charge to 80 or 90%?”
The answer must be kept in the same context as the question, otherwise ot will loose its value.

Also, even if charging to 20 or 50% is the best, Tesla will never be very clear with this as they probably would be sued by owners finding the real range of the car with 20% SOC is not as the advertised range.

One important thing is that Teslas cars/ batteries in the very most cases will hold up for the warranty period.
The batteries will probably hold longer than so in many cases.
There is no real need to do anything than what Tesla write in the manual. Imoortant to read that by yourself as the forum myth put many more statements in the manual than whats really there.
If you only follow the few simple Tesla advices, the battery will not brake. But you probably will have a larger degradation than what is the lowest possible.

OP asks about what cycling strategy that will give the lower degradation, small or large cycles. The truth is small cycles gives less degradation.

Tesla says that we always should keep the car connected, this will give us small cycles.

Ask the folks who recommend 50% how much range are they expecting to add to the battery. Is it a year? a month? or a mile. No one really knows.

You do not add range, you slow down the loss of range due to degradstion.

The 55% or below charging target advice will cut the calendar aging in half compared to 60% or more.
Having the car at low SOC during the most of the day keeps the calendar aging low.
One good strategy is to not charge in the evening but late in the night so it is finished relatively shortly before the next days drive, keeping the SOC low during the night and the time with high SOC shorter.
This chart is valid for EV cars with NCA batteries. The research results in litterally hundreds of research reports tell us this.
The rate of calendar aging might possibly be slightly less in latest gen. batteries but the data we get from real cars do not show that. Instead it follows the research quite well.

Below the step you cut the calendar aging in half.
Calendar aging is the main degradation source during the first 5-8 years of a battery life. Cyclic aging is a minor part for most EV owner.
So, in the end you cut the degradation in half, that is what you can expect.
If also charging late and keeping cycles small you can do better than that.

The rate of Calendar aging reduce with the square of time, so the first year loss will take four year in total to double. If a high SOC car looses 12% after four years, the low SOC car would be at about 6% loss.

Even if Teslas warranty is ”70%”, the industry standard is ”80%” and the degradation is less predictable below 80% capacity, so I would try to keep my battery well above the 20% loss mark. I guess there will be cars no one wants to buy in the furure due to weak batteries, so keeping the battery fresh calls for a better value when selling it in the future.

I have used the low SOC stategy since my M3P was new, two years and two months ago and almost 60K km / 37 K miles.

The dips in range is not real range dips but the BMS that was off track. Current range at about 490 km is close to the ”real” range. (Last full charge was 498km).
The average M3P ’21 at teslafi is about 465 km range, so they have lost some 8% in average range.
My car has 490-498km, thats 3.3 to 2% range loss.

 

[AAKEE]

If keeping it at 50% is only going to make a 1% difference over 10 years, perhaps it's not worth even talking about it. appreciate the discussion from everyone -

It is a matter of reducing the calendar aging. Having the car at or below 55% (for NCA Chemistry, like long range cars) will cut the total degradation in half.

For someone (really) needing 80%, if charging late so it finish shortly before the drive, and driving the car down to low SOC, this still will give low calendar aging.

 

[AAKEE]

Why does Tesla allow setting it down to 50% if 90% is so magical and perfect and ideal and everyone should just charge to 90%?

We know this. Both from science/ research but also from what Tesla put in the update notice the day they changed to the 50-90% slider we have today.

Note the text about longevity.

 

[Drinyth]

We know this. Both from science/ research but also from what Tesla put in the update notice the day they changed to the 50-90% slider we have today.

Note the text about longevity.

I hadn't seen those images before. Thanks for sharing!

Given the slider change and verbiage ("to maximize battery longevity, only charge to the level needed") was provided directly from Tesla, that's rather telling that their research supports there being a difference between the high and low daily charge values.

 

[AAKEE]

I hadn't seen those images before. Thanks for sharing!

Given the slider change and verbiage ("to maximize battery longevity, only charge to the level needed") was provided directly from Tesla, that's rather telling that their research supports there being a difference between the high and low daily charge values.

Just to rub it in, I’ll throw in another source from Tesla

This text is found in every application for EPA certification Tesla makes. They can be found on the EPA Website.

 

[Midnightsun]

Problem with home charging to 50% all the time is when you actually need range such as in an emergency you are screwed because it will take hours to put in more. Personally I charge to 90%, plugged in at home and at the office almost all the time. I simply love the fact my car is always full when I drive off and one of the advantages of owning an EV. Not worth the short comings trying to squeeze every once of battery longevity out of the pack.

 

[RedY23]

Why does Tesla allow setting it down to 50% if 90% is so magical and perfect and ideal and everyone should just charge to 90%?

Freedom to do as you please...even if it does not include reading the manual!?

 

[RedY23]

Just to rub it in, I’ll throw in another source from Tesla

This text is found in every application for EPA certification Tesla makes. They can be found on the EPA Website.
View attachment 913801

Storing a battery is a vastly different situation than using a battery. But let all the non chemists chime in with non research.

I would have to guess, I am only a non chemist non chemical engineer...a typical forumite... but I think that has to also do with safety. Less energy stored in case of some catastrophe?....but not too low as charge state as to not damage the battery.

 

[Drinyth]

Problem with home charging to 50% all the time is when you actually need range such as in an emergency you are screwed because it will take hours to put in more. Personally I charge to 90%, plugged in at home and at the office almost all the time. I simply love the fact my car is always full when I drive off and one of the advantages of owning an EV. Not worth the short comings trying to squeeze every once of battery longevity out of the pack.

Fair point. If your EV was your only vehicle and you were worried about needing maximum range at the drop of a dime, I could see the desire to keep it charged to 90%.

I do have the luxury of having two other ICE vehicles in my garage that I could use in such an emergency situation. If I suddenly needed to be someplace as fast as possible and that was outside the range that a 50% charge on my vehicle would take me and it couldn't wait for me even to stop at a supercharger for a few minutes to top off, I could always use take a non-EV car. In all my years of driving, I can honestly say that I've never had a situation come up where I suddenly needed to drive anywhere >150 miles away with no notice.

But my use case is certainly not the same as yours. I can see others who might need max range at a moments notice and for those folks, by all means, charge to 90% on the daily. Everyone should charge their vehicles as it suits them and to their own needs.

I do love the fact that my car is always charged back up to the capacity that I'll need it for every morning. For me, 50% is "full' enough for my daily needs. Not needing to regularly refuel at gas stations and being able to plug in at home and have it "full" the next day is definitely a nice advantage of owning an EV.

 

[Drinyth]

Freedom to do as you please...even if it does not include reading the manual!?

Storing a battery is a vastly different situation than using a battery. But let all the non chemists chime in with non research.

I would have to guess, I am only a non chemist non chemical engineer...a typical forumite... but I think that has to also do with safety. Less energy stored in case of some catastrophe?....but not too low as charge state as to not damage the battery.

Excerpts from the manual have been quoted in this thread. The FAQ has been quoted in this thread. Various portions of research papers have been pasted into this thread along with numerous other documentation authored by Tesla.

I'd argue that plenty of evidence has been brought forth to indicate that SoC does have impact on battery longevity. Whether it's worth modifying ones SoC levels to maximize battery longevity is a personal decision that can only be decided by that individual.

 

[AAKEE]

Storing a battery is a vastly different situation than using a battery. But let all the non chemists chime in with non research.

No, it is not.

During time of usage, the battery is subject to calendar aging also. Anyone think the aging of time stops just bu using it?

Anyway: Most cars is driven for one to three hours a day, or less. Charging is also one to five hours or so.
(15000km a year takes 300 hours at 50 km/h average, less than one hour each day.
Charging that energy (3000kWh) back takes 2 hours a day with 4kW.
The rest of the day, 20 hours the var is stored.)

I would have to guess, I am only a non chemist non chemical engineer...a typical forumite... but I think that has to also do with safety. Less energy stored in case of some catastrophe?....but not too low as charge state as to not damage the battery.

”To maintain service life, the battery pack should be stored….”

So, Tesla was not clear enough in that sentence?

All Teslas advices is in line with the research. It all match, but not with the myths.

 

[AAKEE]

Problem with home charging to 50% all the time is when you actually need range such as in an emergency you are screwed because it will take hours to put in more.

You should not use a lower charging target than the SOC you need. That includes emergencies or a sick mother-in-law some hundred miles away. And range anxiety.

 

[Dr. J]

a lot of what Tesla says has more to do with marketing then with engineering.

Or possibly with warranty expense, customer support expense, and rescuing stranded drivers expense. I believe, based on no evidence, that Tesla's battery charging advice is driven much more by these corporate expenses than by Tesla's concern with the consumer's battery longevity (as long as the battery survives the warranty period). That seems rational.

 

[RedY23]

Excerpts from the manual have been quoted in this thread. The FAQ has been quoted in this thread. Various portions of research papers have been pasted into this thread along with numerous other documentation authored by Tesla.

I'd argue that plenty of evidence has been brought forth to indicate that SoC does have impact on battery longevity. Whether it's worth modifying ones SoC levels to maximize battery longevity is a personal decision that can only be decided by that individual.

SoC MYP ? We sound the the FAA here. Find Another Acronim!
But Whatcha talking about? Of course what happends between you and your battery is personal?!?
All I said is that the charge state for a storred battery may also have something to do with how much energy that battery should hold in store and higher energy state may be dangerous… also too low a state bad for chemistry(different chemical issues).
Comparing the numbers quoted for said stored battery pack to how a normal batery should be used is a bit like comparing aao(apples and oranges). I think the top number at least has more to do with safety?

 

[RedY23]

No, it is not.

During time of usage, the battery is subject to calendar aging also. Anyone think the aging of time stops just bu using it?

Anyway: Most cars is driven for one to three hours a day, or less. Charging is also one to five hours or so.
(15000km a year takes 300 hours at 50 km/h average, less than one hour each day.
Charging that energy (3000kWh) back takes 2 hours a day with 4kW.
The rest of the day, 20 hours the var is stored.)


”To maintain service life, the battery pack should be stored….”

So, Tesla was not clear enough in that sentence?

All Teslas advices is in line with the research. It all match, but not with the myths.

Yup battery pack stored in stacks of two. If you are storing def would use that advice. But if the pack is in a car used regularly it does not mean optimum life is achieved in the storage batery number range.
Thats all I am saying.

 

[E90alex]

Yup battery pack stored in stacks of two. If you are storing def would use that advice. But if the pack is in a car used regularly it does not mean optimum life is achieved in the storage batery number range.
Thats all I am saying.

Anytime you’re not actively using the car or charging the car, the battery is being stored. So for most people the battery is being “stored” for 80-90% of the time even with daily use.

If 50% is good for the battery for long term storage, then it ahould be good for the battery for short term storage as well.

Obviously usability plays a role for daily use so you don’t want to lower the charge limit to the point of inconveniencing yourself, but many people would be more than fine with a 50% limit daily.

 

[STS-134]

Problem with home charging to 50% all the time is when you actually need range such as in an emergency you are screwed because it will take hours to put in more.

Just what kind of emergency would require you to drive ~130-180 miles on zero notice? Seriously. And if there's truly an emergency (i.e. you're being evacuated) you're going to get a lot closer to the EPA range than you do driving at 80-90 mph, because you're not going to be able to go 80-90 mph. If you just mean doing a trip on short notice, well, it's pretty easy to get from 50% to 100% in less than 4 hours (more like just over 3.5 hours), and from 50% to 80% in approximately 2 hours. But even then, there's no scenario where I've ever had to go more than 50-100 miles in an emergency.

 

[E90alex]

Just what kind of emergency would require you to drive ~130-180 miles on zero notice? Seriously. And if there's truly an emergency (i.e. you're being evacuated) you're going to get a lot closer to the EPA range than you do driving at 80-90 mph, because you're not going to be able to go 80-90 mph. If you just mean doing a trip on short notice, well, it's pretty easy to get from 50% to 100% in less than 4 hours (more like just over 3.5 hours), and from 50% to 80% in approximately 2 hours. But even then, there's no scenario where I've ever had to go more than 50-100 miles in an emergency.

A sudden drop of the hat emergency with zero warning that not only requires you to drive 150+ miles away, but also you can’t stop at all even for ~15 mins to top up at a supercharger (likely also while eating or using the restroom).