Scheduled battery preheating vs. battery degradation

[AAKEE]

This is very interesting, thank you very much!

I use a 2018 Model S, no heatpump, so it seems that the heatpump makes a huge difference.

Actually I use scheduled charging with 5kw, this makes the car to charge during the night in multiple session, each lasting for approx. 40-50 minutes, adding 3-4kwh to the battery, then no charging for half an hour and so on.
Then in the morning it still actively preheats the battery, so it seems that my charging pattern is not even enough to keep the battery warm with the waste heat, not even in 0C degrees.

Model S/X before the heat pump works different and and least as I understand it, use the battery heating more often than model 3/Y and the new S/X.

Did you use ”charge at low cost” selection togheter with scheduled charging?

The M3P I had before and the MSP I have now does not charge in several sessions for scheduled charging, or scheduled departure. They only do it in one chsrgikg session from start to finished charging.

The minimum battery temp for charging both these cars is higher than the battery temp target for preheating the car, so if the charge is recently done the car will not use the battery heating when starting the drive or using preconditioning.

(For older S/X without the heat pump it might be better to charge at arrival.)

 

[bumcurriculum]

Did you use ”charge at low cost” selection togheter with scheduled charging?

As far as I see in the app, off-peak charging and scheduled charging are mutually exclusive.

So I use scheduled preconditioning and off-peak charging. (this morning was special, I set the scheduled preconditioning departure time to a too late time accidentally, so I started the climate manually before the charging was complete)

Also, today the off-peak charging happened in one stretch, not in the roughly one hour stages as yesterday. (there was in fact enough time to perform it in stages, but the car decided to start later, and do it in one stage)

 

[bumcurriculum]

(For older S/X without the heat pump it might be better to charge at arrival.)

Is there any specific reason for that?
I am using the off-peak charging for two reasons:
- keep the SoC lower for longer, to minimize calendar aging(I charge to 55% on weekdays for a 20% commute, and to 90% on weekends to be prepared for any unplanned travel)
-hope to have the battery somewhat warmed by the charging, apparently not at perfect temperature, but maybe somewhat warmer than without this.

 

[AAKEE]

Is there any specific reason for that?

I havent bottomed that really. Keeping an opening for that.

People that are into saving electricity think charging when arriving and then driving with no preconditioning later say that saves the energy.

But for heat pump cars we know the consumption differs very much in cold between a warm and cold battery.

 

[Quickst]

battery heated with dragstrip mode to +13- +14C

In most places in Australia the minimum temp does not go below 0C on most winter days and we dont have heated garages for the same reason.
Its a pity that a non P Tesla 3/Y is not able to schedule preconditioning that includes increasing battery temp to 20C.

What does scheduled preconditioning do to battery temp?

 

[AAKEE]

In most places in Australia the minimum temp does not go below 0C on most winter days and we dont have heated garages for the same reason.

We average around 0C annually where I live,

What does scheduled preconditioning do to battery temp?

For my M3P it was about 5-7C.

My current MSP does only to about 5C

Its a pity that a non P Tesla 3/Y is not able to schedule preconditioning that includes increasing battery temp to 20C.

If you charge late, so the car is just finished when its time to leave, abd charge with the max power you can prefeably 11kW), the battery might get over 20C.

I do that in my garage (just did), the garage is heated to about 10C.
Cell temp on ny M3P often reached 27-28C at 100%, the amount of kWh you add of course
My Plaid has a larger batt so it gets less counted in centigrades but the energy in kWh still is about the same, or slightly more.

My MSP reached 100% a little less than one hour ago and reached 21.5C.

 

[Justjim]

I only get the nocite that says about ”cabin temp ready” but never saw no ”turn off” suggestion, during three years and two different cars.
Live in a very cold climate (-40C right now) so I’m used to precondition.

I read in the manual, I think, that the battery doesn't like -30C and will automatically protect itself by keeping the battery warm. I've noticed the battery loses maybe 5% per day in winter. For example, the interior is saying -6C and I'd look again and it's rising, to about +3C. Tesla service told me this amount of loss is normal as the car protects itself in winter and also excessive heat in summer (battery cooling). I have a 2016 X. They never suggested that I have to preheat before driving, but could for comfort. But then who can you trust? Talking to one guy at the SC, I was getting answers that didn't make sense to me. Finally, I asked him how long he'd been working for Tesla. He said proudly, this is my second week! I waited for the other guy to come back and got "different answers".

 

[Justjim]

In most places in Australia the minimum temp does not go below 0C on most winter days and we dont have heated garages for the same reason.
Its a pity that a non P Tesla 3/Y is not able to schedule preconditioning that includes increasing battery temp to 20C.

What does scheduled preconditioning do to battery temp?

I believe it circulates the "coolant" through the heater to warm the battery. And conversely cools it when too hot. The warming also happens when you enter directions to a charging station. Tesla recommends entering a charge station any time you are going to one inorder to "precondition the battery". This will save you 10 minutes on charge time. If the battery is not preconditioned, it will start by preconditioning, which is sloooow.

 

[Justjim]

As far as I see in the app, off-peak charging and scheduled charging are mutually exclusive.

So I use scheduled preconditioning and off-peak charging. (this morning was special, I set the scheduled preconditioning departure time to a too late time accidentally, so I started the climate manually before the charging was complete)

Also, today the off-peak charging happened in one stretch, not in the roughly one hour stages as yesterday. (there was in fact enough time to perform it in stages, but the car decided to start later, and do it in one stage)

How long is your off-peak time period that you have to charge in 1 hour periods?! Ontario, where our conservative government has sold off public generation to take away the cheapest power in the country (6 cents/kWh any time of day) to give us the most expensive power in the country (new peak rate is 22 cents/kWh). But our off-peak is from 7pm to 7am, at around 11 cents/kWh.

 

[bumcurriculum]

No off-peak period here, flat rate electricity 24/7.
I set the off-peak charging in the car just to delay charging to keep it at lower SOC for longer.
Then the car itself decides to charge in multiple shorter periods for whatever reason...

 

[Justjim]

No off-peak period here, flat rate electricity 24/7.
I set the off-peak charging in the car just to delay charging to keep it at lower SOC for longer.
Then the car itself decides to charge in multiple shorter periods for whatever reason...

Just curious, what's your cost for power in Euros? The conservatives with some help from the liberals have screwed up our system so bad, we can't actually control production like when we had coal plants. Excess power that we paid too much for, we have to PAY adjacent provinces and USA states to take! Contracts are just coming to an end that paid CDN $0.82/kWh for solar and 0.46 for wind. Current cost in US for wind is about 0.04! GO FORD! (go to hell)

 

[AAKEE]

I read in the manual, I think, that the battery doesn't like -30C and will automatically protect itself by keeping the battery warm.

No.

For my M3P (2021) and my Plaid (2023) that is not the case.

I live in a cold climate (-28C right now) and even if I mostly have the car in a warmed garage when at home, it also is outside in very cold for about one week at the time at work. I did have my car parked at weeks with -30C.
The battery do not cool of very fast, so I have let it down to -20C without any battery heat at all running, before activating charging to heat the battery.

I've noticed the battery loses maybe 5% per day in winter.

I have about the same loss at very cold temps as I see at summer.
Thats 0.1% SOC / 0.1 kWh per day.

Do you know that the car displays lower SOC when the battery is cold than the real SOC?
You can look at the app for this, the blue part of the charging level (normally green) is the part of the energy not availsble when the battery is cold.
2-5% is normal, I saw 8-9% difference or so when the battery was -20C.

This is my battery right now. Car was in the garage overnight but I went away for some hours and left it outside (working on my Audi in the double garage now).

This can be seen by comparing scan my tesla where I can see the real SOC with the displayed SOC.
It is easy to see in teslafi as well:
The car has/measures 43% but shows 41% on the display.
Cell temp was 5C when I parked it ~ one hour ago.

For example, the interior is saying -6C and I'd look again and it's rising, to about +3C. Tesla service told me this amount of loss is normal as the car protects itself in winter and also excessive heat in summer (battery cooling). I have a 2016 X. They never suggested that I have to preheat before driving, but could for comfort. But then who can you trust? Talking to one guy at the SC, I was getting answers that didn't make sense to me. Finally, I asked him how long he'd been working for Tesla. He said proudly, this is my second week! I waited for the other guy to come back and got "different answers".

I do not know that much about the older gen of S/X, but i have three years of logging model 3 P 2021 and my plaid.
I have also connected SMT to a few other 3/Y.

The battery is never kept warm when the M3P or MSP is parked. Connected or not do not make any difference. (Caviat, I only let the battery cool down to ~ -20C before starting to charge just to get the battery heating running.

You know that when the car sleeps the big battery is disconnected and no battery heating is possible (?)

Having logs about when my car has been sleeping or not shows when battery heating could not have happened at all.
(My logs of scan my tesla mostly stops after a day at very cold when the tablet shut down from being too cold, if I leave it in the car).

Day after I arrived at work, very cold:

Day after that. It was below -30C and I connected the UMC at ~ 6A/230V to heat the battery. Before that the battery was approaching -20C.

The charging was stopped the day afyer without any gain in SOC, but cell temp ~ 0C


Ther rest of the days, cold but not below -30C (like -15- -25C) looked like this:

Some days, the car wakes up briefly and charges the LV-batt:

The car did fall asleep at 40% on friday, and woke up and charged the LV-battery as per above at 39.4%. The time awake seem to have been 10-20minutes, and no battery heating was done.

As per the people at the service centers, they seem to spread as much myths as the rest of us owners, so I would not thrust their knowledge on these parts.

 

[bumcurriculum]

Just curious, what's your cost for power in Euros? The conservatives with some help from the liberals have screwed up our system so bad, we can't actually control production like when we had coal plants. Excess power that we paid too much for, we have to PAY adjacent provinces and USA states to take! Contracts are just coming to an end that paid CDN $0.82/kWh for solar and 0.46 for wind. Current cost in US for wind is about 0.04! GO FORD! (go to hell)

In Hungary, we have a special rate system where households pay an artificially low electricity cost, and in exchange every goods, services etc. are taxed to hell, and we had 35 % inflation in the last two years, etc... Household rate is 0.18Eur, SUC price is 0.44Eur. The electricity provider buys my solar excess production for 0.013 (!) Eur.
It makes no sense to compare these numbers to a market economy.

 

[Quickst]

I believe it circulates the "coolant" through the heater to warm the battery. And conversely cools it when too hot

Yes it can do that. However, I am not seeing "scheduled preconditioning" increasing battery temp to operational temp. Ive noticed that typical battery temps immediately after normal driving is around 35⁰C (this to me indicated operational temp) Scheduled preconditioning does not increase battery temp to this.

Come to think of it, it probably does not need to as there is always waste heat from battery, motor and inverter usage, so if a battery gets heated to operational temp, there is no where for the waste heat to go. So its wasted electricity.

I think "Scheduled Precon" is only important for extreme cold conditions like @AAKEE's winter ("extreme" for me ) and maybe LFP batteries which tend not to work well around -10 to 0⁰C IMO (regen limited)

 

[Geir]

The question in this case was regarding scheduled departure that also heats the battery vs not heating the batt and possible extra degradation from that.

(This kind of battery preconditioning is not the same, it just heats to be able to use regen.)

OK, but what do you think about precondition before supercharging? is It better to shut It off if you are not in a hurry? Could It be better for the battery to charge at lower speed? I search for Superchargers with the lowest effekt bequase I think this is better for the battery life.

 

[AAKEE]

OK, but what do you think about precondition before supercharging? is It better to shut It off if you are not in a hurry? Could It be better for the battery to charge at lower speed? I search for Superchargers with the lowest effekt bequase I think this is better for the battery life.

I always precondition fully when possible.
All research shows that lithium plating (the bad part of fast charging) is minimized by heating the battery to > 40C before the charge session.

Tesla heats the battery during the session as well. And low SOC is less suspectible to lithium plating and esla reduce the charging power if you have a cold battery, but better to be safe than sorry and always precondition fully.

 

[Quickst]

Could It be better for the battery to charge at lower speed

Slow charging is always better. 1C = the charging rate required to completely charge a battery pack from 0-100% in 1 hour.

So for a 75kWh battery pack charging rates equating to C:

250kW 3.3C
75kW 1C
50kW 0.66C
25kW 0.33C
11kW 0.15C
2.4kW 0.03C

For a 50kW battery pack
50kW charging rate = 1C

Anything below 1C is considered to be good for minimising effects of fast charging.

Thats why a Tesla Mobile connector is an excellent way to charge despite being slower than the Wall Connector.
Many people want to charge as fast as possible but there is often no need especially with overnight charging before the morning drive.

While high temps are not good for Li-Ion batteries in the long run, on balance, it is better to heat up the batteries so it can be charged properly. In any case most supercharging sessions are typically 30minutes - not long enough for high heat to negatively affect battery life. Once the car is driving the temperatures will settle to a more normal temp.

lithium plating (the bad part of fast charging)

Yes

Because the anode is not warm enough to accept lithium ions from the cathode and the lithium metal builds up on the surface of the anode.
A warm anode allows lithium to inside the anode and take part in the required chemical reaction
Fast charging at cold temps is certain to cause lithium plating - the chemical reaction at the anode is not fast enough due to low temps so lithium builds up on the surface)
Fast charging at optimal warm temps can also cause lithium plating especially at higher SoC
Plated lithium can be reversed but not a 100% - the plated lithium is lost to the charging process, reducing overall battery capacity. The plated lithium is eventually encapsulated in SEI - solid electrolyte interphase making it completely invisible to any charging/discharging process.
A high power discharging mode at C>1 could possibly reverse to a degree lithium plating but there is no mode like this at the moment.

DCFC is best with warm batteries at low SoC and well designed battery management systems that regulates charging speeds as SoC rises

 

[AAKEE]

Slow charging is always better. 1C = the charging rate required to completely charge a battery pack from 0-100% in 1 hour

Yes, with the exempt that it below a certain C-rate the cyclic aging does not reduce by reducing the C-rate further.

This is Panasonic NCA cells with ~2.9A capacity.
1A (~ 0.3C) and lower currents cause the same cyclic aging.

So all AC charging will have about the same cyclic aging. There are more examples of this in the research but these charts show this in a clear way.

While high temps are not good for Li-Ion batteries in the long run, on balance, it is better to heat up the batteries so it can be charged properly. In any case most supercharging sessions are typically 30minutes - not long enough for high heat to negatively affect battery life. Once the car is driving the temperatures will settle to a more normal temp.

Yes, the positive effects by fast-charging a heated battery is multiple times better than the negative fast-charging a cold or non heated battery.

Yes

Because the anode is not warm enough to accept lithium ions from the cathode and the lithium metal builds up on the surface of the anode.
A warm anode allows lithium to inside the anode and take part in the required chemical reaction
Fast charging at cold temps is certain to cause lithium plating - the chemical reaction at the anode is not fast enough due to low temps so lithium builds up on the surface)
Fast charging at optimal warm temps can also cause lithium plating especially at higher SoC
Plated lithium can be reversed but not a 100% - the plated lithium is lost to the charging process, reducing overall battery capacity. The plated lithium is eventually encapsulated in SEI - solid electrolyte interphase making it completely invisible to any charging/discharging process.
A high power discharging mode at C>1 could possibly reverse to a degree lithium plating but there is no mode like this at the moment.

DCFC is best with warm batteries at low SoC and well designed battery management systems that regulates charging speeds as SoC rises

We know that Teslas BMS is supposed to be very good, but still there is compromises.

I once ended up needing a charge which became evident about at the time passing the last SuC station (only, actually).
There was a new christmas layout on the screen (2021) so I couldnt even find the suc to activate preconditioning.

Cell temp ~ 12C, and the charging went straight up to ~130kW (V2 supercharger) so more than 120kW netto after deducting battery heating
I had low SOC ~15% and lithium plating mostly occurs higher up so probably not that bad but the feeling was not good.

 

[Quickst]

In Australian summer, battery temps are sometimes high enough to not require supercharging preheating. This causes some drivers to be confused and assume something is wrong or broken. It would be a nice Tesla software update that indicates "preconditioning not required" when battery pack temps are adequate.

Thats why a Tesla Mobile connector is an excellent way to charge despite being slower than the Wall Connector.

I should have added "in cold temps approaching freezing". I have not found studies looking at battery degradation at 0celcius using various C. I suspect in this case even lower C rates is preferable.

One of the reasons that charging at less than 1C is better than more than 1C is that there is less graphite(anode) electrode cracking. There are other reasons too. But don't let that stop supercharging from time to time because most charging (for most people) is home charging which is always way below 1C

 

[AAKEE]

I should have added "in cold temps approaching freezing". I have not found studies looking at battery degradation at 0celcius using various C. I suspect in this case even lower C rates is preferable.

Tesla has a temp buffer, so no charge before the cell temp is ~ +3C, then the max allowed charging increases quite fast allowing for regen etc.

Charging with DC doesnt happen until ~ +3C, and even with low power like 2-3kW my M3P kept the cell temp at ~8C (heating going on/off to keep that temp).
My plaid keeps +5C in the same condition.

This is from a research report about lithium plating. (It is not a very nice graphical way of showing this, as it might seem that it gives the same capacity loss anyway)

What we can see is that we need ~ +25C for 1C charge rate and that we would need to reduce the charging rate successively with reduced temp down to 5C. (The SOC also matters, but as a general info. This was not panasonic cells so not exact our type of batteries but we get an indication of how it works).