What Percent is Your Tesla Charged to While at Home?

[zoomer0056]

what determines SOC

Like a politician once said, "It depends on what the definition of "is" is."

To question 2, it depends on when the calculation targets. The calculation can target anytime. An important number is the average SOC. If battery is charged to 55% and is run to 45%, or the daily routine keeps the average SOC around 50%, then 50% would be the number used.

 

[PACEMD]

For our new 2023 M3P I charge to 50-60% when at home and only driving locally. And if I don't need the power soon I dial the wall charger down to 12 amps and charge slower. On my weekly commute of 150 miles to work, I charge to 90%. Seems to be a good strategy to vary that home % number, 50-80%, and when you can let it trickle in. I was a little less careful with our 2019 M3P- but it's still running strong at 70k miles and has only in theory lost 7% range. Understand those numbers are not entirely real.

 

[PACEMD]

Curious how you picked 52%

Me too, also. I've heard 53% is much much better..........

 

[PACEMD]

Oh, and my slow charging as above, probably doesn't matter. But it makes ME feel better. Isn't that what it's all about?

 

[3sr+buyer]

If I am travelling and I let it go to 3% before supercharging to 80%, is that bad? I've not wanted to stop in certain areas and skipped the SC for the next one, but if there is a specific "don't go below %" (limited understanding is that it's fine as low is good).

Low state of charge is fine as long as you do not run out completely.

 

[BigNick]

You do not have to micromanage the battery pack. The BMS will keep your battery healthy for you, with acceptable degradation per Tesla specs.

If you do choose to micromanage the battery pack, you can beat the BMS in terms of preventing degradation. But this requires more effort (and possibly expense, such as air conditioning a hot garage) on your part and some may not find it to be worth their time, money and effort.

 

[AAKEE]

Got through all 20 pages and still need simplified answers.

1. The difference between SOC of 55% vs 80% is roughly 2% per year degradation, is that a correct conclusion?

Nope.
Its more like whatever degradation you hsve at 80%, 55% will cut that in half.

First year might give about 5-6% degradation for many people, so 2.5-3% less.
After X years when the 80% would have 15% degradation, the 55% car would have 7.5%

2. So here is the part I don't particularly understand. Is there a time of non-use involved in determining SOC? If I charge it to 65%, and it sits for 30mins before I leave, then get to work and it's at 55% and it sits for 8-10hrs, wouldn't that be the SOC, 55%? Or is it whatever you charge it to initially the SOC? I guess I'm wondering what determines SOC % in the calculations in the thread.

When driving (or charging) the SOC can not be really measured. That is because the SOC is defined by the open circuit voltage (OCV) or resting voltage.

SOC displayed while driving needs therefore to be estimated/calculated.
Example: Having 100% and a estimated capacity of 100 kWh, then after using up 50kWh we should have 50% SOC left.
After parking the OCV is measured and the real SOC is displayed.
After each drive and each charge the SOC is measured when the car is at rest and the SOC is updated. For short drives we probably do not see any difference but after a long drive it might be, if the BMS capacity estimation is not spot on.

3. If I am travelling and I let it go to 3% before supercharging to 80%, is that bad? I've not wanted to stop in certain areas and skipped the SC for the next one, but if there is a specific "don't go below %" (limited understanding is that it's fine as low is good).

Its not bad.

In general, low SOC is god.
From one of the latest research tests the wear is slightly higher below 25% or so, but the cyclic wear is anyhow very low.
You can use the whole SOC range as you like or need.

I use low SOC often and down to ~0% whenever I need.

There are a few simple rules to minimize degradation. I do not list them in this post though.

4. Lastly, what happens if one were to SC to 100%?

SC = Service Center, SuC = Supercharging I guess.

Superchsrging to 100% is not dangerous.
The car reduce the charging speed at higher SOC’s, so for the last 10% its rather slow.

 

[Apprunner]

Me too, also. I've heard 53% is much much better..........

I do 53%...its because it fluctuates by 1-2% after I finish charging. I figure i won't exceed 55% if it goes wonky afterwards. Sounds like a lot of us are OCD

 

[DrChaos]

Got through all 20 pages and still need simplified answers.

1. The difference between SOC of 55% vs 80% is roughly 2% per year degradation, is that a correct conclusion?

No, roughly the degradation rate is half otherwise all else being equal. (and SOC needs to stay below 55%). The models scientifically show calendar degradation going as sqrt(time). So it's like 1/2 sqrt(time) vs sqrt(time) but that's entirely an empirical approximation and what is happening underneath is complex---it's probably a few different processes, some of which degrade linearly and some degrading much slower or even capped and they're all mixed up.

In a real car battery with all sorts of other effects and use I think the degradation difference between < 55% and 80% charge limit will be smaller but still present, maybe 35-40%? Also people who set charge limit to 80% are varied in their driving habits, some may drive more (and have lower state of charge) so they will feel like degradation is low (as they mentally calibrate per mile like ICE cars), but those who charge from 75-80% every day and think they are "babying" their car will have more degradation than they expected.

For example, I kept my car's limit at 50% for all but about 10 days in my first year. I had degradation from 358 miles when new to about 342 in 12 months, that's 4.4%. Temperatures were moderate. Less than 5-6% typical 1 year but more than half of typical. And of course BMS calibration uncertainty adds to this.

2. So here is the part I don't particularly understand. Is there a time of non-use involved in determining SOC? If I charge it to 65%, and it sits for 30mins before I leave, then get to work and it's at 55% and it sits for 8-10hrs, wouldn't that be the SOC, 55%? Or is it whatever you charge it to initially the SOC? I guess I'm wondering what determines SOC % in the calculations in the thread.

the scientific tests are at constant SOC, so it's time weighted. The idea is that there are chemical reactions happening at the graphite anode all the time, very slowly. That rate depends on state of charge. So the length of time that it sits the longest matters the most.

3. If I am travelling and I let it go to 3% before supercharging to 80%, is that bad? I've not wanted to stop in certain areas and skipped the SC for the next one, but if there is a specific "don't go below %" (limited understanding is that it's fine as low is good).

It's fine for occasional use. There was a paper AAKEE found recently that surprisingly shows more cyclic degradation around 0-20% and suspected that was from the silicon doping in the graphite anodes as used in higher capacity/advanced NCM/NCA batteries (which probably includes Tesla). But again, these were tests that repeated the same thing over and over and over to emphasize the difference. If you're on a road trip like a normal personal car owner, emphasize your comfort and safety for sure, you won't see any difference. It's the day to day which matters.

4. Lastly, what happens if one were to SC to 100%?

There is a bit more cyclic degradation going up in the 90-100%. But if you do this infrequently it doesn't matter that much.

The only place cyclic degradation is really going to matter heavily is in energy storage or intensive commercial trucking where they are going to push through most of the battery capacity every day.

 

[DrChaos]

I do 53%...its because it fluctuates by 1-2% after I finish charging. I figure i won't exceed 55% if it goes wonky afterwards. Sounds like a lot of us are OCD

And remember that 50% displayed on a Tesla screen is more like 52.25% in science papers because there is a lower 4.5% buffer below displayed 0% vs scientific 0%. So 53-55% displayed on Tesla might be uncomfortably close or at the shelf in degradation rate, I use exactly 50% to try to be below it.

 

[AAKEE]

The central graphite peak is at 57-58% on a new panasonic ncr18650 of the kind they tested dome years ago.
Calendar aging mainly reduce the capacity above the central graphite peak so the SOC level for the central graphite peak will increase with time.
So 55% is safe for the ~57-58%.

Also, the exact position of the central graphite peak will depend on the chemistry.
We have examples with tests showing that 60% is ”safe” for some NCA cells.

 

[pdx_m3s]

My thinking on this topic...

Here's what we know: Higher SOC and heat are causal in cell degradation. Where possible, try to keep both down.

For me, I charge to 50% in the summers and 60-65% in the winters. I also try to always park in the shade during the summer and garage my car at home, which also has the benefit of a cooler cabin and seat in the summer.

When needed, I have no problem charging to 100%. Car is 4.5 years old and sitting at ~8% degradation.

 

[kimwin]

I am new too, only 3 weeks with my M3SR. Charging to 80% every few days, 100% a week.

 

[AAKEE]

I am new too, only 3 weeks with my M3SR. Charging to 80% every few days, 100% a week.

You could either charge like ypu do now or charge to 100% every time,

Or, if the reason to charge to 80% is that you try to reduce degradation, then 70% or less would be a better option.
80% and 100% will most proabably be very close in terms of degradation but 70% will make a difference to the better.

 

[3sr+buyer]

Or, if the reason to charge to 80% is that you try to reduce degradation, then 70% or less would be a better option.
80% and 100% will most proabably be very close in terms of degradation but 70% will make a difference to the better.

80% versus 100% could help if you drive off and use (for example) 15% and then park the car for a while (at 65% or 85%). But that is a less effective way of trying to avoid degradation than charging to 70% or less unless more is needed for the amount of driving before the next charge.

 

[PerformanceEV]

There are a few simple rules to minimize degradation. I do not list them in this post though.

I have just read through this entire thread and would really appreciate a simple post outlining the 'few simple rules to minimise degradation'. Is this something you would be willing to share please @AAKEE ?

I have recently purchased a used Model 3 Performance, one of the main reasons I chose the car was for its performance, so I am trying to weigh up whether charging to a maximum of 55% and helping reduce battery degradation is worth it given the significant drop in performance according to the dyno tests carried out by Mountain Pass Performance - their tests showed that from 75% to 45% – a 30% drop in SOC, results in a massive 64 horsepower difference! (see dyno graph below) I must say I was a bit disappointed to learn that the drop in power with SOC is a feature of EVs!

My typical work commute would use less than 10%, so to enjoy near on peak performance I would really need to charge to a minimum of 85% daily.

Would you be able to estimate in actual full charge mileage loss how the below scenarios would compare, taking into account battery degradation over a period of 3 years and 60k miles on a 2 year old M3P with 25k miles? e.g. Scenario 1 estimated 10 mile loss vs Scenario 2 estimated 20 mile loss

Scenario 1. Charging to 55% every night. Normally from 45-50%
Scenario 2. Charging to 85% every night. Normally from 75-80%

Is it advisable to charge every night to keep DOD to a minimum? Even if the battery is only discharged 5-10% in a day?

 

[AlanSubie4Life]

I have just read through this entire thread and would really appreciate a simple post outlining the 'few simple rules to minimise degradation'. Is this something you would be willing to share please @AAKEE ?

It is possible to reduce the degradation by about 50% (without any big sacrifice) by applying the known facts from research:
- Use low SOC when possible. Below 55% cut the degradation from time in half.
- Charging late, like in the morning before the drive instead of when arriving in the evening before reduce the time at higher SOC.
-Do not charge more than you need (including a margin for range anxiety).
- Charge often - the smaller each cycle the smaller the degradation from cycles.

5. Low SOC is NOT dangerous. Below 20% is safe and do not cause increased wear. It actually reduce the calendar aging.
100% SOC is not as bad as the forum myth says. You do not need to drive asap. The degradation is about the same at 100% as at 80-90%.

From here, more details there. Just one of several such summaries.

Would you be able to estimate in actual full charge mileage loss how the below scenarios would compare, taking into account battery degradation over a period of 3 years and 60k miles on a 2 year old M3P with 25k miles? e.g. Scenario 1 estimated 10 mile loss vs Scenario 2 estimated 20 mile loss

I think for this it would be necessary to know a bit about how degraded your car is already. So would need to know 100% SOC extrapolated rated miles, as compared to 315 mile starting point (2021 or newer).

But the good news is that due to the age, the absolute magnitude of the loss difference you'd be looking at will be quite a bit smaller than it is for a new car. (Meaning the damage is probably already mostly done, though there are still probably some small benefits to be had from optimization.)

Rule of thumb (possibly slightly optimistic) is a 50% improvement (reduction in range loss), though.

is worth it given the significant drop in performance according to the dyno tests carried out by Mountain Pass Performance - their tests showed that from 75% to 45% – a 30% drop in SOC, results in a massive 64 horsepower difference! (see dyno graph below)

Keep in mind that these charts at low speed are not correct (not sure why). The torque doesn't behave that way and it doesn't increase with speed at low SOC as is seen around 30-35mph in these plots. All the power curves should lie roughly on top of each other up to 30mph (which they don't here).

Anyway, this power drop is definitely noticeable - I use 55% and I do notice it, but the good news is that up to 30-35mph, it makes very little difference. Torque and power will be the same up to about 30mph over a very wide range of SOCs. It's the power at high speeds that changes. The acceleration at low speeds will be quite similar, since peak torque is relatively insensitive to SOC. Once above 35mph or so, you'll start to notice differences due to SOC, if we're talking about the ~50% vs. ~70% comparison.

Personally, though, I find 300HP adequate for daily driving. Of course 500HP would be better but if I really want to drive hard, I charge to a higher level. Having the massive peak torque off the line, nearly regardless of SOC, even if my peak power is quite low, is nice too.

A couple of links to pictures here (AWD) and here (Performance) and here is a relevant Reddit post (which includes one of these plots in the comments):

https://www.reddit.com/r/teslamotors/comments/dqxnqt

Google for Reddit posts and you'll find a lot of instrumented data, especially from wugz.

 

[nicksp]

I wonder what is the average number of years people will keep their EVS. Is all of this strict charging regimen to make sure the battery doesn't degrade below a certain threshold? Why not rely on the 8 year warranty Tesla offers?

 

[dcfas]

I tried charging to 70% for a few weeks. It was enough most of the time, but now and then it got too close for comfort. 80-85% gives me peace of mind.

 

[zoomer0056]

I wonder what is the average number of years people will keep their EVS. Is all of this strict charging regimen to make sure the battery doesn't degrade below a certain threshold? Why not rely on the 8 year warranty Tesla offers?

Charging to 55% daily works great if one doesn't need more miles than that. Charge more when needed. The warranty is a backup and is activated for a defective battery.