Range Loss Over Time, What Can Be Expected, Efficiency, How to Maintain Battery Health

[nvesprini]

Hi everyone

Does anyone know the actual mechanism for how depth of discharge damages the battery? Im interested in what is actually going on with deep vs shallow charge cycles.

Eg: let's say I have a battery at 20% soc. Would it be better to:

1)charge up first to 60, let the car sit for a while, then continue from 60-100% (effectively two separate charging sessions of 40%)

OR

2)go from 20-100 in one shot (one large 80% charging session).

Not looking to make this a regular habit, just trying to better understand whatever is going on to damage the battery with deep cycles.

TIA

 

[BobHinden]

I don't think it will make any difference. Though, of course, you don't want to be charging to 100% on a regular basis.

 

[AAKEE]

Hi everyone

Does anyone know the actual mechanism for how depth of discharge damages the battery? Im interested in what is actually going on with deep vs shallow charge cycles.

Eg: let's say I have a battery at 20% soc. Would it be better to:

1)charge up first to 60, let the car sit for a while, then continue from 60-100% (effectively two separate charging sessions of 40%)

OR

2)go from 20-100 in one shot (one large 80% charging session).

Not looking to make this a regular habit, just trying to better understand whatever is going on to damage the battery with deep cycles.

TIA

1 and 2 will cause similar wear.

A cycle is one charging session and one discharge. So, basically the ”round trip” for the battery. Splitting the charge cycle do not change anything.

While it is called ”Dept of Discharge” and the term ”deep cycle” is commonly used its actually the high state of charge part that wear more than the low part.

We could imagine the battery being a baloon inflated with air. The term ”stress” that people often use in conjunction withh batteries is when it is inflated. The more inflation, the more the stress.

Well, back to the battery:
If you have it at 20% which is good, and is to charge it it will be the time at high SOC that causes the most wear. This means that charging as late as possible will cause the lowest degradation.

The cycle dept, how big the cycle is, is causing less degradation the smaller the cycle is, but also less the lower the cycle is placed. Two smaller charging sessions is better than one large.

 

[tb.dxb]

Looks good and follow our plan to hit ~79 kWh

While its not probable that it goes way above 79 kWh, the energy screen is limited to the maximum range number = 79 kWh. This means that if the capacity goes above about 79 kWh, the calculation will still show about 79 kWh.

Yes!
Just hitting 1,360 miles, I reach 79.1 kWh

Keeping SoC around 55% most of the time, unless I have one of my 175 miles round trip. Charging up to 70 or 75% at departure, reaching back home typically around 25%. I think I am pretty close to the EPA reference, off by roughly 10% - I guess mostly A/C consumption penalty, since our temperature is 35 ~ 45 C (AFAIK, EPA is measured at 24 C ?).

 

[AAKEE]

Yes!
Just hitting 1,360 miles, I reach 79.1 kWh

Good to hear! We was expecting it, but anyhow a good follow up post!

On a fun note, my new S Plaid started at 75.3 kWh, out of 99.4kWh full pack when new.
I soon found that it would need to climb to 98.0 kWh, as I could calculate the capacity to be about 78kWh. I only needed one longer drive to find this out, the BMS needed three weeks.

Now we ( me and my BMS) are on speaking terms at 98.0 kWh

Keeping SoC around 55% most of the time, unless I have one of my 175 miles round trip. Charging up to 70 or 75% at departure, reaching back home typically around 25%. I think I am pretty close to the EPA reference, off by roughly 10% - I guess mostly A/C consumption penalty, since our temperature is 35 ~ 45 C (AFAIK, EPA is measured at 24 C ?).

23C (I think*), AC /ACC Off.

There also is a cold WX test at 20F that is included in the tests and thats weighed in into the consumption that leads to a certain declared range.


There is a lot of discussion about certain cars/brands that is closer to the EPA (or WLTP) range.

The tests include some part (about 40-50%) driving in the city, rest is highway and also the 20F part making the end result a consumption that is a mix of s lot of things.

What it is not, is a real range on a highway.

*) Possibly a mix up in my mind as WLTP is also tested at 23C.

 

[Quickst]

Lowest possible setting is 50%.

Of course - the auto charging stop minimum is 50%
I'm finding that 3 times a week charging to 50-55% will give me a lowest SoC of 25% before charging.
I don't think range anymore. Can't remember when was last time I looked at available km by pressing the battery icon.

 

[tb.dxb]

What it is not, is a real range on a highway.

For sure.
However, I am surprised so far that highway driving seems to be still more efficient then city driving, at least at a certain cruising speed (say, 72 mph / 115 kmh). Considering the one pedal drive, regen and TACC I expected consumption to be more even, but I noticed some 50% more in city traffic. If I take city driving into my calculation then I am off by approx 30% and this is not all A/C.

I'm finding that 3 times a week charging to 50-55% will give me a lowest SoC of 25% before charging.
I don't think range anymore. Can't remember when was last time I looked at available km by pressing the battery icon.

Yes, I think I get a hang of estimating the consumption for a certain trip, then pre-charge accordingly to hit back home or the destination with 20~25%.

 

[blodg8]

Hello,

Since I got the Model 3 for about a week. Its a used 2018 with only 49,150 miles on it. I just started driving it yesterday for the day and I drove about 40-45 miles and I noticed my battery drained from 88% to 55%. I had the AC on probably 60% of the time. I didn't check what was the estaimated miles but when I came home it still have 157 miles left with 55% battery. Is my battery draining correctly and is not degraded? just odd and maybe I'm not used to seeing the battery drain on a car...

 

[Quickst]

Is my battery draining correctly and is not degraded?

That is hard to know without further information
Note that the displayed % is just the computer (battery management system) trying to estimate the actual remaining range that is in the battery. It is not necessarily displaying the actual range

Generally the actual miles driven has little to do with the battery degradation. The age of the battery (2018) has a more significant effect despite the low miles. The low miles just means wear and tear on the car (apart from the battery) is expected to be low.

Suggest trying a BMS reset (AKA recalibration):

 

[johnny_cakes]

Also, as a data point, I've attached the degradation of my '21 LR at 70k miles. (I think I got lucky).

That looks really good. Just a warning though, you may want to double check the degradation number as Tessie has a tendency to under report it as was the case with my car. The current capacity that it shows is the current "nominal" capacity, while by default the original capacity that it compares against may be the original "usable" capacity (or in my case what it thought was the original "usable" capacity calculated from an incorrect original "nominal" capacity). Tessie allows you to customize the original capacity so you can compare it properly. To verify the accuracy of the measurement, you can compare the "Max Range" that Tessie shows just below your screenshot. Compare that to the original EPA range estimate of your vehicle. If the drop in max range relative to original EPA estimate aligns closely with the degradation number that Tessie shows, you'll know it's accurate. If it's way off, you'll want to adjust the original capacity accordingly.

 

[johnny_cakes]

I just watched a presentation from Jeff Dahn (

)

He did not say anything strange.
He showed the work on lithium batteries that could do very many cycles.
All was tested down to 3.0V (which was considered 0% on those cells). He is impressed himeself.

View attachment 932309

Jeff Dahn discusses battery health last week in this video:

Takeaways:

• Degradation is higher at higher SoC. "If you go away in the summer, store at a low state of charge (30%)"
  • He chose 30% because you'll still have range when you come back from your trip.
• He said "Lower the state of charge, the better" during the Q&A. He didn't say how low you can go and still be safe.
• Stick to low depth-of-discharge. "Charging frequently to ensure lots of low DoD cycles is better than charging infrequently, leading to high DoD cycles"
  • After 2.5 years of continuous testing (equivalent of 1.5 M km travelled), cells that did 25% DoD only lost 8% capacity, while 100% DoD lost 27% capacity
• Higher the temperature, higher the degradation. "The colder it is, the longer your battery will last, as long as it's not doing anything"
• If you have a Ni-rich battery (most common with long range EV), only charge to 75% if you can
• For the following types of Li-on batteries, impact of these optimization strategies is minimal so they can be ignored:
  • LFP
  • Single crystal positives with Ni content < 70% (e.g. NMC532, NMC622)

Last but not least: even if you ignore all of these recommendations, your battery will be fine.

Lots of great info in the video - worth watching!

 

[AAKEE]

Jeff Dahn discusses battery health last week in this video:

Takeaways:

• Degradation is higher at higher SoC. "If you go away in the summer, store at a low state of charge (30%)"
  • He chose 30% because you'll still have range when you come back from your trip.
• He said "Lower the state of charge, the better" during the Q&A. He didn't say how low you can go and still be safe.
• Stick to low depth-of-discharge. "Charging frequently to ensure lots of low DoD cycles is better than charging infrequently, leading to high DoD cycles"
  • After 2.5 years of continuous testing (equivalent of 1.5 M km travelled), cells that did 25% DoD only lost 8% capacity, while 100% DoD lost 27% capacity
• Higher the temperature, higher the degradation. "The colder it is, the longer your battery will last, as long as it's not doing anything"
• If you have a Ni-rich battery (most common with long range EV), only charge to 75% if you can
• For the following types of Li-on batteries, impact of these optimization strategies is minimal so they can be ignored:
  • LFP
  • Single crystal positives with Ni content < 70% (e.g. NMC532, NMC622)

Last but not least: even if you ignore all of these recommendations, your battery will be fine.

Lots of great info in the video - worth watching!

Interresting!

I have had to ”defend” what I learned like litterally one hundred times as people did find some older videos where Jeff Dahn recommended 70% or something like that.
Actually I already did think ”Oh no, hete we go” before I saw the new approach

Very good! Then I just need to refer to this new approach instead of a lot of explaining text.

 

[melvladimir]

highway driving seems to be still more efficient then city driving, at least at a certain cruising speed (say, 72 mph / 115 kmh)

I guess you have heavy feet) Or maybe you don't use recuperation as much as you can. BTW, somehow it's more tricky than I expected, still learning.
Here are my results (summer tires Michelin Primacy 4+ 18" with aero caps, 3.1bar):

• 100 km/h constant speed is slightly better than the estimation (my M3LR '22 shows 100% = 551km): 135Wh/km
• normal city driving (neither "chill" nor "fire emergency"): 130-140Wh/km
• chill city driving within speed limits: 110-130Wh/km
• 115 km/h = ~160Wh/km

I like to step on the accelerator all the way down, but after that, I itch to use recuperation. That's how I get 150Wh/km on average (ACC on, headlights on)

 

[johnny_cakes]

Interresting!

I have had to ”defend” what I learned like litterally one hundred times as people did find some older videos where Jeff Dahn recommended 70% or something like that.
Actually I already did think ”Oh no, hete we go” before I saw the new approach

Very good! Then I just need to refer to this new approach instead of a lot of explaining text.

The takeaways from his latest video are very consistent with the other research reports you've read

 

[Jejunjm]

Degradation seems high for a vehicle that's only 2 years old with a low average SoC, even in the hot Arizona climate. I wonder if the BMS is out of calibration.

Agree :/ I'm going to run it to low and do a battery health in service menu for interest. It's very hot in Tucson though so maybe real. The first few months, in summer, I had it I charged it to 80 unnecessarily. Oh well, live and learn

 

[AAKEE]

Agree :/ I'm going to run it to low and do a battery health in service menu for interest. It's very hot in Tucson though so maybe real. The first few months, in summer, I had it I charged it to 80 unnecessarily. Oh well, live and learn

I think I have a way of checking the real battery capacity quite easy.
It do not require Scan my Tesla (SMT) but the result might be slightly more precise if it is used.
The displayed range can be used also.

The simple explanation is to find the size of the fault of the SOC estimation the BMS does during a drive.
To find this, a single longer drive is needed.

The SOC is estimated during a drive as it can not be measured. If the BMS estimated capacity is wrong, the estimated SOC will be wrong. After a drive, when the battery is at rest or almost at rest the real SOC can be measured and BMS can update the SOC.

If the BMS is spot on, the SOC doesnt change afterwards:

Here’s one example where the BMS underestimated the battery capacity.
Knowing the “end of the drive displayed SOC” and the “after a sleep SOC” and the used energy during the drive we can calculate the true capacity.
Below the readjustment can be seen:

SMT helps calculating it very precise
When parking:

After the sleep

We can do this with the displayed range as well.
Each km or mile is a specific energy, so a increased range or reduced range after the sleep means we can calculate the change in SOC quite precise.

I’ll be back with the calculations later.

 

[Quickst]

@AAKEE
My MYLR 2023 giga Shanghai went to sleep 2 days ago
The SoC at the start of the sleep was 30%. This was just after arriving home from 70km drive = end of drive SoC
2 days later I opened door and pressed brake. The SoC is 29% no sentry = after a sleep SoC

I will drive it 60km without charging on Sunday. At end of drive I will charge to SoC 50%. Let me know what screenshots you want of the energy app

 

[AAKEE]

@AAKEE
My MYLR 2023 giga Shanghai went to sleep 2 days ago
The SoC at the start of the sleep was 30%. This was just after arriving home from 70km drive = end of drive SoC
2 days later I opened door and pressed brake. The SoC is 29% no sentry = after a sleep SoC

Looks like the BMS is about spot on.

I will drive it 60km without charging on Sunday. At end of drive I will charge to SoC 50%. Let me know what screenshots you want of the energy app

60 km might be a little on the low side, I guess. I would prefer to see 150km or 100 miles driven. Just using the SOC/range we probably need a longer drive.
It probably also is better to drive at a decent speed and not too fast.
I have done all my checks on drives to the work, 240km.
But even with only 60km driven, if we see a change in range after the drive it is a indication as from the describtion below.

If the BMS was way off, it would probably be enough to show if it was over- or underestimating.
In your case, as you ”only” lost 1% after two days, your BMS is probably showing about right.

The basics for this is:
We expect the BMS to be spot on = no change of SOC/displayed range after the sleep.
Range decrease after the sleep = overestimation of the capacity.
Range increases sfyer the sleep = underestimation.

This version is a simplification from doing the same with Scan My Tesla which will give a more precise result. I did a few double checks from the displayed range and they basically show the same result as with Scan My Tesla, but as the resolution is lower, so a longer drive would compensate for this.
——————————————————————
Before the drive, let the car sleep (after the charge etc) to make it record the correct ”true” SOC. This is important as we need a BMS starting the estimation from a correct SOC.
After the drive you should record these numbers after the drive:
-SOC and range (in km) at end of the drive. Take this value asap, before any readjustment happens.
-Used energy for the last drive. The total kWh might be fine but [distance x average consumption] gives a more exact result.

-After the car has been parked/locked/sleeping for 30 minutes or more: -SOC and range (in km).

The change in range (or SOC) after the sleep indicates the BMS capacity estimation error.

Each change in range/km = about 0.15kWh, or the actual constant for your car.

(Used energy +/- delta energy)/(Used energy) = the correction factor for the BMS estimated capacity / range.

For example:
Used energy = 50 kWh
Range decreased from 100 to 93km after the sleep = 7 km delta = 1kWh.

(50-1)/50 = 0.98.
The true capacity is 98% of the BMS estimated capacity.
The BMS is overestimating the capacity if this number is below 1, and underestimating if it’s above 1.
Displayed maximum range or calculated capacity from the energy app can be adjusted by multiplication by the correction factor.
——————————————————————
We expect the change in range to be very low. No change means the BMS is estimating the capacity correct.

I’ll be back later with the use of Scan My Tesla to calculate the capacity.

 

[fcrunk91]

That looks really good. Just a warning though, you may want to double check the degradation number as Tessie has a tendency to under report it as was the case with my car. The current capacity that it shows is the current "nominal" capacity, while by default the original capacity that it compares against may be the original "usable" capacity (or in my case what it thought was the original "usable" capacity calculated from an incorrect original "nominal" capacity). Tessie allows you to customize the original capacity so you can compare it properly. To verify the accuracy of the measurement, you can compare the "Max Range" that Tessie shows just below your screenshot. Compare that to the original EPA range estimate of your vehicle. If the drop in max range relative to original EPA estimate aligns closely with the degradation number that Tessie shows, you'll know it's accurate. If it's way off, you'll want to adjust the original capacity accordingly.

Noted! My range at 100% shows 340 miles. The original EPA rating of 353 aligns with the Tessie, 96.3% capacity.

Now that I see that video by Dr. Dahn, I would guess that it would be prudent to keep your garage cool in the summer, maybe?

I plan on buying a house soon, probably with a detached garage. What are some easy, cost-effective ways to keep a garage chilly in the summer? I feel as though an EV battery would benefit greatly if it could be stored at cool room temperature when not being driven.

 

[johnny_cakes]

Noted! My range at 100% shows 340 miles. The original EPA rating of 353 aligns with the Tessie, 96.3% capacity.

Now that I see that video by Dr. Dahn, I would guess that it would be prudent to keep your garage cool in the summer, maybe?

I plan on buying a house soon, probably with a detached garage. What are some easy, cost-effective ways to keep a garage chilly in the summer? I feel as though an EV battery would benefit greatly if it could be stored at cool room temperature when not being driven.

Wow, amazingly low degradation. Congrats!

Your car would certainly benefit from being in a garage, but cooling it to prevent battery degradation may not be the best use of resources. While I'm open to adopting a low SoC strategy, I've accepted that ambient temperature and time are two factors beyond my control.