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

[STS-134]

Tesla is clear that the range at the battery symbol is showing the energy content and not actual range. This is the choise Tesla have made.

If they're showing energy content, then they should show it in a unit of energy. You know, kWh, joules, etc.

The real range is shown at the energy app, and that one is good on estimating the actual range from the average of the last 10/30/50 km (and equivalent for miles).

Now that's interesting. I didn't even realize that. So there's obviously an issue with making sure people know about this feature.

 

[STS-134]

The self discharge from a lithium battery is very low. This means that when the battery disconnect itself by the contactors (as it also does during a sleep) the drain of the battery is very slow.
Tesla warns about the low voltage battery can be damaged, because it will discharge quite quickly when not charged. Lead acid batteries wear bad from discharging too much and I think some 50% SOC is the safe level for these.
So the lithium battery in a Tesla that shut down is safe for some further time(quite long time). I would not recommend trying to find the time though.

For calendar aging, lithium batteries is better of the lower the SOC is down to zero %. Note, that this is discharged to the safe level, 0% SOC but still within the minimum voltage level. From this they are left in that state for about a month or two in the research tests, then a few cycles and discharge is performed to find the capacity and after that they are charged or discharged to the SOC they use in the test.
In this test the battery cells is left as the test SOC( 0% for the 0% points) for two to three months without getting damaged, they actually have the least degradation despite 2-3 months a time at 0% SOC, and 10 months in total.
View attachment 799982
This picture show the calendar aging for NCA, NMC and LFP cells. While it is a recent test, and other tests show the same, we actually do not have data on the absolute newest battery cells. But as the basic chemistry do not change very much for each type we can use these results as a base for understanding the degradation frm time on these battery types. In some cases the newest cells might have slightly reduced (or increased) cyclic aging or calendar aging.


For LFP there is a need to charge full to reset the BMS energy counter on a regular basis. LFP has very flat voltage curve and the BMS counter of the actual remaining stored energy might drift and in the worst case you find yourself stranded when the battery goes empty despite the BMS did think there still was plenty left.

LFP suffer from calendar aging but as you can see the calendar aging is not that bad at 100% for specially shorter periods.

We can expect LFP cars to have slighty less degradation for the same use, just to give a number about half compared to LR and P cars. This because calendar aging is the dominant degradation factor for both types.

This is actually also possible to see in teslalogger.de/degradation. The LFP versions seem to loose about half the range per driven miles/km. In reality the calendar aging comes per time and not km/mile but there is no such graphs.
Its also a bit early to say for sure as LFP has not been around in Teslas for that long, but the facts we have from research points in that direction.

Based on all of this info, I have lowered my charge limit for daily use to 50%.

 

[Bouba]

Based on all of this info, I have lowered my charge limit for daily use to 50%.

I’m at 55% mostly because it’s a nice round number of 300 km range

 

[AlanSubie4Life]

So there's obviously an issue with making sure people know about this feature.

Yes, the Energy App is quite informative. Really it's only important to use the Trip Planner page, though, which is automatically used when you navigate to a destination even if you're not using the Energy App. I never use the Energy Consumption screen (with the 5/15/30-mile intervals on it); it doesn't provide much everyday utility, except as a check for your consumption constant and the capacity of your battery (which are important, but not on the daily).

they should show it in a unit of energy

Rated miles are a unit of energy (a variable size unit depending on the vehicle, lol). Admittedly, the name makes it sound very much like a unit of distance, but it's not really. But if you just go with this fact, it makes everything much more comprehensible - and it's also very easy to figure out how many Wh are in each one.

 

[MP3Mike]

The in-car range estimate is not required to use the same result displayed on the sticker AFAIK. Nor are car manufacturers prohibited from publishing a 2 dimensional range chart with speed on the x-axis and range on the y-axis.

Because people would be so happy if they bought a car that had 330 miles of range on the sticker but the display only showed 250 when they picked it up. Look at how many people come here to complain about it going down just 5-10 miles...

Tesla used to have a widget on the web where you could put in speed, temperature, AC setting, etc. and it would show you the predicted range. But they took it away at some point.

 

[rjpjnk]

If they're showing energy content, then they should show it in a unit of energy. You know, kWh, joules, etc.

I’ve been saying this as well. The “range” shown by the battery icon is really just energy remaining times a fixed scal factor for the particular model of car. So yes, it is really an estimate of energy and I’d like to see an option at least to display it in some standard units of energy as you said. I would prefer kWh over Joules since that matches the battery units.

 

[Bouba]

I’ve been saying this as well. The “range” shown by the battery icon is really just energy remaining times a fixed scal factor for the particular model of car. So yes, it is really an estimate of energy and I’d like to see an option at least to display it in some standard units of energy as you said. I would prefer kWh over Joules since that matches the battery units.

It does have a percent option...you can’t get any more clearer than that

 

[AlanSubie4Life]

It does have a percent option...you can’t get any more clearer than that

Percent is unitless though, so it tells you nothing, other than what portion of your maximum energy you have left. No units.

 

[AAKEE]

Percent is unitless though, so it tells you nothing, other than what portion of your maximum energy you have left. No units.

Yes, at least at some other places theres usually a hard battle if the km/miles or percent should be used.
A degraded battery still shows 100%, but it will not even do 100% of the lower-than-EPA practical range it had as new.
The km/mile scale actually show the energy content (In a odd scale, but it does).

 

[Bouba]

Tesla could mimic an ice car and just say...full...three quarters...half...quarter...empty

 

[rjpjnk]

Tesla could mimic an ice car and just say...full...three quarters...half...quarter...empty

True, and this is pretty much the same as percent of course. The problem is, with a battery your “gas tank” is getting smaller as the car ages.

To take the ICE analogy one step further, a battery meter that measured in kWh would be like a gas gauge that measured in gallons. I would much rather know how many gallons I had left than just “half full”.

 

[rjpjnk]

Percent is unitless though, so it tells you nothing, other than what portion of your maximum energy you have left. No units.

Exactly. It is like a gas gauge not telling you how many actual gallons remain, just that the tank is 25% full. It’s still very useful, but gallons would be even better because that tells us the actual quantity.

This is exactly why I’d like to have an option to display battery in kWh.

Showing battery in units of miles is a poor choice scientifically, but it give us a sense of a real world quantity we can relate to for now. People are not yet familiar with a reading of energy units remaining, but I think we will be as EVs become more popular and transactions in the fuel business in units of kWh becomes more typical.

 

[scottf200]

Showing battery in units of miles is a poor choice scientifically, but it give us a sense of a real world quantity we can relate to for now. People are not yet familiar with a reading of energy units remaining, but I think we will be as EVs become more popular and transactions in the fuel business in units of kWh becomes more typical.

Love built-in NAV miles because you can compare them to predicted miles on the energy screen.
Great when helping passengers be more comfortable on road trips as well. Have used it for 100K of road tripping.

How to accurately predict range in a Tesla

How to accurately predict range in a Tesla

gregsramblings.com

 

[STS-134]

True, and this is pretty much the same as percent of course. The problem is, with a battery your “gas tank” is getting smaller as the car ages.

Well to the extent that an aging engine consumes fuel less efficiently, the same thing happens with ICE vehicles too.

 

[MP3Mike]

True, and this is pretty much the same as percent of course. The problem is, with a battery your “gas tank” is getting smaller as the car ages.

There are some years of Prius where the gas tank actually does shrink, especially in cold. By up to 50% if I recall correctly.

 

[conv90]

I have done a couple of discharges to try to lower my NFP. This because I was more or less certain that the BMS overestimated the capacity because of my charging schedule.

First one, late last summer down to 0.4% did not change the NFP noticeble.
Second one down to -1.8% did change the NFP down with about 1.5 kWh.
Third one -2% did set it down to the same NFP as the second one.

What I learned was that after the second one the NFP climbed back quite quickly from about 79.5 kWh to 80.5-81 kWh.
After the third one the NFP initially stayed at about the same value, then I realized that the charging schedule was very tight to the drive to the work. Earlier I always had one and a half hour or two with the 55% charge finished, letting the car sleep with 55%.
When changing the schedule back to give a sleep after the charge the NFP started the climb up immediately.
I also have found that not using Sentry at work increase the NFP further.

I am at the opposite side, normally having too high NFP, and the factors that keep the NFP up cannof course be used in that purpose.
- Let the car sleep as much as possible, after charging.
- Shut of Sentry when possible

In my case, these actions and my charging schedule will cause an overestimate of the capacity, but it might take some time.

I have not fully undertand:
I was thinking you were charging the car to 55% at night and START to use the car immediately after the end of the charge (or as fast as you can).
Then you say that you had to change habit letting it (instaed) sleep another 1,5 to 2 hours before to use it to go work?

What I wanted to say with my posted graphs (here the update one at today) is that it seems IMPOSSIBLE to determine the ACTUAL kWh capacity even having SMT, because the flutuations are too big.

In my example, which is the correct kWh capacity of my march 2021 82.1 kWh "Full Pack When new" Pana Battery? 73,8-73,9 (the february level after 11 months?) OR the 77,7-77,8 kWh (the January level ) Or the 77,8 (the level of NOW)?
OR probably it's something in between? (76,00kW?).
If someone ask to me, which is the level of degradation of your car battery after 14 months? I have to reply : " Im not sure, it's Between -2,6% to -8%"
What I wanted to say is that we are nerds enough to look at the fraction of the Watts, and using millivolt precision to judge things, then we have results where there are 4 kWh difference between readings.

 

[rjpjnk]

I agree. The fluctuations are too extreme to say much about battery degradation with resolution any better than about +- 5%. Btw, I have a very similar capacity chart as yours with a big drop in Winter and recovery in Spring. Not sure what the weather is like where you are but here in NJ USA I am fairly certain the temperature fluctuation has influenced the capacity estimation performed by the BMS. I do not know what the formula is, but I am happy that mine has also appeared to have "recovered" as yours has. It is nice to have this data recorded but I highly doubt it indicates that my battery somehow reversed itself and began becoming "healthier" after a while. It is more likely just a demonstration of how meaningless the data is on any short term scale.

 

[conv90]

I agree. The fluctuations are too extreme to say much about battery degradation with resolution any better than about +- 5%. Btw, I have a very similar capacity chart as yours with a big drop in Winter and recovery in Spring. Not sure what the weather is like where you are but here in NJ USA I am fairly certain the temperature fluctuation has influenced the capacity estimation performed by the BMS. I do not know what the formula is, but I am happy that mine has also appeared to have "recovered" as yours has. It is nice to have this data recorded but I highly doubt it indicates that my battery somehow reversed itself and began becoming "healthier" after a while. It is more likely just a demonstration of how meaningless the data is on any short term scale.

View attachment 802081

I really don't know if temp has a rule. Sure yes but not directly linked . I'm in North Italy and the winter can be real cold with always under 0° C (32°F) at night with january the coldest month .
But I had the other max value in january (77,8kWh) and the worse values in february/march when the temps started to rise up to 20°C .
It's your car a LR with the 82.1 Panasonic Batt?

.

 

[AAKEE]

I have not fully undertand:
I was thinking you were charging the car to 55% at night and START to use the car immediately after the end of the charge (or as fast as you can).
Then you say that you had to change habit letting it (instaed) sleep another 1,5 to 2 hours before to use it to go work?

Yes, the absolute best for the battery would be as short time as possible after charging.

I decided early that I would try to keep the degradation low, but not try so hard that it made the EV ownership a pita.

So I calculated that some times I might use more than ususal and have less SOC than usual and that should not cause a need to change the schedule. So I set a margin for that, about 50km extra driving or about one hour of extra charging( 11kW). Also, sometimes I need to leave a bit earlier to work so I did set the charging to commence 0300 or 0330 depending on the season. A regular day I use about 20-25% or so, so that would make the charging finished around 0430-0500.
I leave around 0630 a regular day.

Then, recently, I had the charging set to commence later, causing almost no time between the charging finished and the drive to work. This was not really done for any reason but the BMS seem to have calculated the NFP lower and there was not an increased NFP after a discharge below 0 until I did set the charging to be ready as before.

What I wanted to say with my posted graphs (here the update one at today) is that it seems IMPOSSIBLE to determine the ACTUAL kWh capacity even having SMT, because the flutuations are too big.

Yes, its not possible to use that info for any credible capacity judgment.

I would take reasonable number for the initial capacity, and then reduce the capacity with the estimated calendar aging according to the NCA graphs.

The question is the initial number. The 2170L seems to vary a lot in the initital number. It is a lot more variation than we see in other battery cell variations. I do not know why.

Most ininitial M3P Fremont built seem to had a initial NFP around 80-81kWh. There is at least some that seem to start with around 77 kWh or slightly more. These seems mostly be built in China.

Not an accusation —> I do not know if Tesla/ Panasonic have started to reduce/ cheat on the formation cycling that normally is done to make the battery cell stable and perform well.

Normally a battery should have the “run-in” done already by the factory, so I think we should not be able to affect the function that much by running the battery in.

Some lithium batteries come with run in process of a initial cycle or two. This is something I will dig into when I have the time, to see if the run in process is ”not perfect” at the factory and if we can affect the battery performance by doing the right
Actions early in the battery life.
I guess Tesla/Pansonic do this as it should be done, but i think these processes take a lot of time. If you have to cycle each pack for a week, maybe you are tempted to start to shorten this of you build a lot of batteries/cars…

 

[Bouba]

Ok..I have grappled with this set of graphs everyday for months and each time I see something different....
Obviously it’s the middle graph of NMC batteries that is most worrying (because I think that is the LG75...my battery)
But graph B almost matches graph A...so I was thinking that is the sudden drop off on graph E might just be it’s temporary loss of storage and not long term damage...because every LG battery would fail the warranty period