Battery Heating explained

Battery Heating explained

So most of my reference data is and Bjorn's videos. I will work to get reference data that will show the specific scenario as written below(FACT paragraph). I am also working to attempt to get data showing heating power vs speed but that is not an easy or quick test.

Ok so here is an explanation of "preconditioning"/"battery preconditioning"/"On route battery warm up".

So all the above terms I am going to simplify as they all mean the action of putting non-motive power to the motor to create heat which then is transferred to the battery through the coolant system. Now the different scenarios as to when this function is activated create differences in how much non-motive power can be applied to the motor(s), and/or what goal temperature the system applies for the battery.

Battery Preconditioning(BC) general description: The Model 3 has the ability to put a non-motive power waveform to the motors in order to generate heat in the Stator(motor). The maximum amount of power applied to each motor is approx 3.5kW. The heat generated is then passed via conduction to the coolant flowing through the motor. This hot coolant then flows to the Superbottle(coolant reservoir). The hot coolant also flows from the superbottle to the battery, and then back to the superbottle.

Lets go through a few scenarios where BC is automatically engaged:

Routing to a supercharger:
When you route to a supercharger and the battery is less than approximately 30°C, BC will turn on and you will get a note on screen that says it is preconditioning. This BC is intended to warm up the battery in order to allow for maximum Supercharging speeds since charging a cold Li-ION battery can damage the battery. When routed to a Supercharger, BC will come on automatically whenever the car feels like it. I haven't found a good correlation on time or distance or variations thereof in reference to battery temperature. I have seen it come on automatically while being over 50 miles away from the supercharger. Now, just because the car "says" it is BC, doesn't mean that it is actually applying the whole 3.5kW(RWD), or 7kW(AWD) to the motor to generate heat. The heating power is greatly reduced when the motor(s) are being used for motion/regen. In a RWD vehicle, the BC power is greatly reduced when going over 40mph. In an AWD vehicle, the BC power to the rear motor is the same as on a RWD vehicle, but the front motor can still get the full 3.5kW as long as it is not being used to move the car. In general cruising on dry roads, the front motor in an AWD vehicle is barely used up to ~90mph.

Preheating Cabin using phone APP:
When the car/battery is cold and you engage climate control from within the Tesla app on your phone, whether you set a temperature, or hit defrost and it goes to max temp, BC will also be engaged(depending on battery temperature of course). The reason for this BC is presumably to help gain some regeneration capability at the beginning of your drive. It would also of course help supercharging speeds if you have to hit a supercharger at the beginning of your drive. I don't know what the target battery temperature for this is yet. On a RWD vehicle, it will apply the 3.5kW non-motive power to the motor to generate heat just like the first scenario above. I would presume that it would apply the 3.5kW to the front motor as well in an AWD vehicle.

So general questions relating to this have been, what is the fastest way to get rid of the regen dots. My general answer to that is, get BC turned on. Heating the cabin in and of itself is going to do practically nothing(this would be getting into the car and turning on climate control and just sitting there.) Turning climate control on via the app should do it, sitting in the car an routing to a supercharger should do it, getting in and setting climate controls and then turning on climate keeping and getting out will do it as well. Now the time to heat the battery up has not been determined yet but that is also going to depend on how cold the battery is in the first place.

FACT 1: In an RWD vehicle, during preconditioning at a standstill, the stator temperature can get from ~24C to over 55C in 10 minutes at ~0C outside temperature. At this point if you start driving at highway speeds, with preconditioning still activated you will see the Stator temp and battery inlet temperatures go DOWN. This indicates that even though the car is still showing a preconditioning condition, it is not actually working.

FACT 2: When you go to a supercharger and your battery is still cold, the car will continue to use BC in order to heat the battery. This is shown by the CANbus messages showing power going to the motor, the stator heating up, and an increased coolant flow rate through the powertrain and battery.

FACT 3: When setting Keep Climate ON in cold weather, after leaving the vehicle, the car will set the battery target temperature to 30C and battery heating will commence as needed.

So I just captured some data on 1/13/2020 in my LR RWD vehicle. Graph is here The graph starts as I am leaving my driveway and ends approximately 5 minutes after I leave the supercharger. I did not stay long at the supercharger, and the 2 little spikes while I was there were me switching stalls in order to ensure the power input was stable no matter what stall I was in. I engaged BC near the beginning as I was going 60 miles per hour. The whole point of this exercise is to show that as you speed up, the preconditioning goes away. This graph shows that as speed increases, the stator temperature levels off and/or goes down. I will also note, that if I had done this trip without BC on, my stator temperature would probably not have gone above ~25°C. Questions welcome. Ohh and yes the radiator was bypassed 100% the entire time.

ADinM3 | 9 januari 2020

@derotam, your thread started out promising, thanks for trying...

derotam | 9 januari 2020

@ADinM3: The comments are irrelevant. This is a data driven OP that needs no comments. Any additional legitimate test data presented by someone else will just be incorporated in the OP.

I posted this as a data reference post that I or others can point others too that have OP relevant questions...just like my other general data thread

ADinM3 | 9 januari 2020

@Derotam, thanks. Stupid me, I kept skiming down this thread and actually forgot to go back to your link in the very first sentence. Good stuff to dig through over lunch...+1.

FISHEV | 9 januari 2020

You want to go back to the range loss of about 20 miles due to Preconditioning over a 20-30 minute run to the SC in 38F. The car is rated 4.13 miles per kWh. So 20 miles of range would be 4.84kWh using Rated Range miles. Probably not ideal miles/kWh so likely more energy that that.

Massive energy spikes with Preconditioning, literally off the charts.

jallred | 9 januari 2020

Nobody wants your input on this thread. You said you would stop.

FISHEV | 9 januari 2020

"You said you would stop."

Sorry...sorry...was just reading it but then I let @Bighorn goad me into pointing out his oft mentioned "45kW" is his own creation, nothing I ever said.

I'll try to be good.

M-A-B-MCMLXXX | 9 januari 2020

Here’s an apt analogy to what the fish is describing above.

Person 1: “1+1.”
Person 2: “Remember when you said 2?”
Person 1: “Nope, I never did; that was your number.”

jallred | 10 januari 2020


I really like these data threads a lot. So I’m trying to keep the bickering down so we don’t lose this thread. I appreciate what you are saying, but let’s see if the truce can hold in this thread.

M-A-B-MCMLXXX | 10 januari 2020

I admire your optimism. I’ll hold my tongue.

jallred | 10 januari 2020

Thanks, I'm prepared for defeat, if it comes.

derotam | 11 januari 2020

Bump as the OP specifically talks about some of the things in other threads on the subject.

derotam | 13 januari 2020

Ok everyone, I just did a test run. Have at the graph and explanation at the bottom of my OP. Questions very welcome. Since people seem to think the car can read minds, I actually did stop at the supercharger so it knew I wasn't trying to trick it.

ReD eXiLe ms us | 13 januari 2020

jallred: When it comes, I won't even notice. ... I'll be too busy lookin' GOOD...

derotam | 13 januari 2020

Added test plan for next weekend. Inputs welcome to ensure appropriate data is collected.

gmr6415 | 13 januari 2020

@derotam, Glad to see you actually did a trip to a supercharger. Boy the things the right motivation can do. Did you video it? Were you far enough out that there was at least some time driving before the pre-conditioning icon came in order to allow the function the full distance it needs to complete the function?

@derotam, "Evidently, some people think that in order to precondition(on-route battery warm up) that is REQUIRED that you actually end up at a supercharger."

Of course. That's what the function was designed to for.

Tesla's definition of on route battery warmup: "On-Route Battery Warmup

"Whenever you navigate to a Supercharger station, your vehicle will intelligently heat the battery TO ENSURE YOU ARRIVE AT THE OPTIMAL TEMPERATURE TO CHARGE, reducing average charge times by 25%."

Notice the word ARRIVE is in there.

@derotam, " I guess the car is so smart that it knows ahead of time that you aren't actually going to a SC and therefore it doesn't precondition(even though it gives the on-screen indication)."

No, but it does know it's on the way to a supercharger and it knows when it arrives, so to do an accurate test you need to drive to and arrive at a supercharger because that's what the function (on route battery warm up) was designed for. You would also need to give it enough distance to perform the full function. I don't think starting 10 miles from a supercharger is going to do it, since I've seen the pre-conditioning icon come on as far as 50 miles out.

You would have to assume it's calculating the amount of warming/pre-conditioning needed from your current location to the location of the supercharger based on, distance to the arrival at the supercharger, current cell temperature vs the optimal cell temperature for optimized charging, all the environmental factors it can get data from, your speed and then decide what it needs to do in order to arrive at the supercharger with the optimal pack temperature.

After all it does state: ...your vehicle will INTELLIGENTLY heat the battery..."

End result, the battery inlet temp and cell temp in your graph are close to the same temperatures Bjorn got when he was doing the same test on an AWD. More so the cell temperature, which would obviously be the most important data point the car is trying to obtain.

Bjorn's data points:

cell temp 26.3

Battery inlet 32.6

5:37 into the video

derotam | 13 januari 2020


jallred | 13 januari 2020


I appreciate you and your data.

derotam | 13 januari 2020

So instead of intelligently asking for specific data points or even attempting to be scientific, you decide to use terms such as "close to the same", and you even seem to say that my alues on my RWD vehicle are similar to an AWD vehicle that has twice the heating capability. Please allow me to now just walk away from the insanity...unless you would like to ask reasonable questions in order to actually understand what is going on.

I can't wait till you get your data logger so I can then just blindly say, well who is to say your logger "compiles" the CANbus data the exact same as Tesla. No I will not do that, because the data is the data and it will either mostly make sense or it will way off from reality.

derotam | 13 januari 2020

@jallred: No problem! If you have any questions or ideas on how to make any of my test better let me know.

gmr6415 | 13 januari 2020

@derotam, When using on route battery warming, the car is trying to obtain the optimal cell temperature for charging at arrival at a supercharger. Plain and simple. That's it.

If it's allowed to do what the function was designed to do by the operator using navigation to navigate to a supercharger without intervention, and it reaches the desired cell temperature for optimal charging when it arrives at the supercharger, what difference do data points make? What difference does it make how it did it? In the end it did what the function was designed to do.

And when I do get my equipment. I'll surely video the whole trip both on the phone and the touchscreen, so people can see the results are true and completely objective...not saying yours aren't, but the more proof the better in this world of doubters.

And yes. I can't count the number of times I've seen a truck operator come into the shop claiming something was wrong with their truck base on a third party reader, then go out and plug in a factory reader and get different results under the same circumstances. Either that or they are getting the correct results but interpreting them wrong. Data is alway subject to interpretation.

gmr6415 | 13 januari 2020

@derotam, "...and you even seem to say that my alues on my RWD vehicle are similar to an AWD vehicle that has twice the heating capability..."

My home unit has an auxiliary electric heating coil should the circumstance arrive that the heat pump can't keep up or if the heat pump fails it defaults to the coil as "emergency" heat.

If it's 40˚F outside, and I set the thermostat to 68˚F and the thermostat has a 3˚F temperature differential setting (will allow the inside temp to go down 3˚F before it turns the heat on), just because the coil (adding additional heating capacity to the heat pump system) is there does it mean it's going to come on? No. The system uses the capacity it needs to obtain the set temperature in a reasonable time.

FISHEV | 13 januari 2020

"I don't think starting 10 miles from a supercharger is going to do it, since I've seen the pre-conditioning icon come on as far as 50 miles out."

10 miles should do it. That's my distance and with battery cold, "Preconditioning Battery for Super Charger" will come on immediately. There will be a huge spike in power usage for the first five(?) miles and then it will settle down so it looks like it does as much heating as fast as it can (NAV tells the car it has 14 minutes to heat up battery) and then waits.

When Preconditioning comes on, I've always been able to pull full power (140kw when available) so the battery must be warmed up in that time/distance 10 miles/14 minutes.

gmr6415 | 13 januari 2020

@FISHEV, What model are you driving? I agree with @derotam that the AWDs have double the potential capacity. At least when it comes to throwing current at the front stator to do the heating. The coolant capacity would be somewhat greater too just because it adds the additional volume from the coolant that flows through the front drive unit.

I don't see how a RWD could do it in 10 miles because most of the heat is going to have to come from inherent internal heat from the various components rather than, or in addition to, dumping a bunch of current at the motor/s.

Bighorn | 13 januari 2020

AWD doesn’t come close to fully heating in 10 miles. I saw 17 kW last time I tried.

FISHEV | 13 januari 2020

“What model are you driving?”


“ I agree with @derotam that the AWDs have double the potential capacity. At least when it comes to throwing current at the front stator to do the heating. “

RWD motor is 340 HP. That is a monster and could generate 75kW of heat and leave 240 HP so the car can rocket around. Does the Tesla state that RWD Model 3’s have or don’t have Battery Preconditioning?

Bighorn | 13 januari 2020


gmr6415 | 13 januari 2020
gmr6415 | 13 januari 2020

@FISHEV "RWD motor is 340 HP. That is a monster and could generate 75kW of heat and leave 240 HP so the car can rocket around. Does the Tesla state that RWD Model 3’s have or don’t have Battery Preconditioning?"

Looks like click bait waiting for someone to ask how you can "tickle" a motor in motion to create additional heat.

FISHEV | 13 januari 2020

“Looks like click bait waiting for someone to ask how you can "tickle" a motor in motion to create additional heat.”

It creates the heat by creating inefficiency in the motor by changing it’s power factor. This creates heat vs. magnetism and it is that waste heat that is channeled to the battery for Preconditioning. There is no dedicated resistive heater as @Bighorn and others mistakenly thought, the heat is created by phase shifting the motor. It was also noted that this works even when the car is not moving, stopped for a light, traffic etc.

Should be easy enough to see on the Energy Graph. Let the battery get cold, 40F should do it, and depleted, 20% should do it, and then drive to within 10 miles of an SC and then NAV to it to turn Preconditioning. You will see a massive energy spike that is off the chart on the Energy Graph. This will go on for about 5 miles and then reduce.

gmr6415 | 13 januari 2020

@FISHEV, Obviously I was right.

jallred | 13 januari 2020

Power factor, heat and magnetism, phase shifting, hocus pocus, abracadabra.

derotam | 13 januari 2020

No point in engaging in this debate. If anyone wants to explain why there was no visible heating effect during my first 60mph section of my graph I would love to hear.

WW_spb | 13 januari 2020

Fish is still clueless. Hahah

jallred | 13 januari 2020


I’ve got a few questions in my mind about your data.

1. Is there a battery inlet temperature set point that is a delta above the current battery temperature? And by setpoint I mean a max differentials?

2. When at speed it appears that the stator temp drops to a specific point and is then held precisely at that point.
Two times at identical speeds it reduces and holds to different temperatures. Is this because the the second time is during preconditioning and the first isn’t? Also, since the same speed can hold at two different temps, is this because the motor is generating more heat the second time or because of different flow rates?

3. Is it possible that they have a target flow rate? And that is the critical control?

They want to heat the battery. To do so you need a inlet temperature that is a function of battery temperature. If the flow rate is trying to be at a constant then you would expect the stator temp to be another specific delta above the inlet temp. I don’t get why the stator temp reduces and then hold tight with such control. I’d really like to see the flow rate. If the flow rate doesn’t change while the stator temp is held constant then that means they have algorithmic control over the motor temp.

Also wonder if you held 60 mph for longer if eventually the stator temp would rise instead of holding fixed.
When sitting still, they create stator heat as fast as possible. At least it appears that way. Maybe generating extra heat while moving has a noticeable affect on performance, so they minimize that.

Would like to see more runs.

derotam | 14 januari 2020


1. I don't know of any metric that defines the differential. I just see that the flow rate seems to increase to maintain a set differential.

2. The different stator temp drop given the same speed is going to be a complicated thing. I think you start getting into a thermal mass conversation and about how the heat dissipates. On my normal 33 mile drive home in ~45-55F outside temp, my Stator will get up to about 30-35C. I would guess that if you let preheat get it up to 40-50C and then drive 60mph, that it will continue to drop to get to the normal thermal load just from driving 60mph. That would take a while though and it wouldn't be linear.

3. I don't think a target flow rate means anything, I think it is goal temperatures. I suspect that if you let preheating go on long enough you would see it stop at a certain point. Possibly it is at a batt temp of ~30C but I have never waited that long, it would take a while.

"expect the stator temp to be another specific delta above the inlet temp"

But it isn't. I have seen my stator get up to 50-60C while the inlet temp and batt temp are both still less than 15C. Now as far as the stator is concerned, I also don't know if there is a max stator temp that can be produced by the constant ~3.5kW heat generating power going in. I don't think you could determine that either since the coolant flow is going to keep increasing which would help to pull more and more heat out...I don't really care about that metric though.

Yes the stator temp could possibly increase. There is going to be an equilibrium somewhere at a given speed and given outside temperature. again, kind of hard to get that data. Lots of time, effort and miles to get that data, and it doesn't really do anything for me.

What kind of runs and for what purpose? I am happy to do multiple runs and spend the time on that data if there is a well defined goal. Doing multiple runs where the speed varies wildly due to traffic or stoplights gives crappy data in regards to anything related to battery pre-heating just because you get in to specific scenario requirements. My whole goal as far as pre-heating is concerned is really to get a pre-heating effect vs speed graph. This in and of itself is a hard thing to do. Trying to compare runs to one another also could be difficult because of variable run start temperatures.

derotam | 14 januari 2020

As far as generating heat while moving affecting's only 3.5kW, that in and of itself wouldn't take much performance away. Now there is the possibility that just the method of adding that power has a overt affect on performance but there is no way to know that unless you can talk to someone about how they are actually doing it.

derotam | 26 januari 2020

Bumping just to keep actual test data front and center while there are more threads getting flooded with misinformation.

FISHEV | 26 januari 2020

"This indicates that even though the car is still showing a preconditioning condition, it is not actually working."@derotam.

derotam | 26 januari 2020

Random small piece of a quote shows what FISHEV, that you still dont understand and want to continue your misinformation.

FISHEV still doesn't even accept that the cars CANbus messages are valid data even though they are provided by the car as written by TESLA engineers.

FISHEV | 27 januari 2020

" In an RWD vehicle, during preconditioning at a standstill, the stator temperature can get from ~24C to over 55C in 10 minutes at ~0C outside temperature"

Wow! That's a lot of power. How many kW does it take to heat the large motor that fast?

FISHEV | 27 januari 2020

"Random small piece of a quote shows what FISHEV, that you still dont understand and want to continue your misinformation."

It was full sentence quote and it was one of your highlighted points in your original post. Seems a fair quote and question in this context of is Preconditioning on during charging.

Whether you or any of the CANBUS crew are qualified to understand and interpret the raw data is problematic as we see CANBUS'ers come to blows over what the data means. Your's was so different from @Bighorn's you thought you had different cars. @grm1915 and you came to virtual blows over some datapoint. And then the various home made 'tests".

It's why Tesla should really be answering these questions with FAQ's vs. all the blind men and their elephants.

Joshan | 27 januari 2020

no they shouldn't... it would only create more confusion. Companies create technology to make things easier for end users not more complex. The car knows what to do, you do not. Let the car do the job it was designed for.

derotam | 27 januari 2020

One sentence lacking the context of the paragraph can mean something different.

FISHEV | January 27, 2020
"Wow! That's a lot of power. How many kW does it take to heat the large motor that fast?"

That would be 3.5kW constant over the 10 minutes, as per the RAW CANbus data shown here Note: The graph is the raw data for anyone to look at and decide what they think it means. How bout you look at that data and give us your interpretation?

And I did not contradict any of Bighorn's CANbus data, since he has none. My data stands alone and I am not trying to compete with anyone. The data is the data and my graphs are just showing the raw data so anyone can analyze it themselves. This is the same data that Tesla is using inside the car to make it's decisions.

derotam | 27 januari 2020

Here's an analogy of FISHEV's thought process... Let's say there is a glass of water that Tesla designed and filled part way. Now lets say that Tesla has a graph that looks like the glass is 50% full. Lets also say that Tesla has constant digital measurements of how much water is in the glass and that is where the data comes from for the graph. Now lets say that someone outside of Tesla is able to look at those digital measurements directly but they actually say the glass is 49.5% full, or even 49.0% full. According to Fish, ONLY the graph is accurate because that is what Tesla has chosen to show the normal user. Fish ignores the source data because it must be wrong, Tesla knows it is wrong, and Tesla must be accounting for it being wrong. This is just stupid.

Bighorn | 27 januari 2020

I would say that 3.5 and 4 kW are in pretty close agreement relative to the insanity of say 48 kW or thereabouts. Utter madness. GIGO

jallred | 27 januari 2020


Found this interesting tidbit, looks like they can use the pump inefficiently to create heat as well.

The waste heat mode may commence with first warming the drive motor fluid pump 204 and fluid to an acceptable operating temperature. In one embodiment, the drive motor fluid pump 204 is submerged in the fluid reservoir 206 and acts as a small heater for the fluid. In such case, the drive motor fluid pump 204 is operated very inefficiently to produce only heat and to produce enough torque to move locally the fluid through the system. A goal in this operation is to transfer heat from the drive motor fluid pump 204 to the fluid as quickly as possible. Once the drive motor fluid pump 204 and fluid are warmed, the waste heat mode may continue to warm the battery 106. Local hot spots allow to drive motor fluid pump 204 to suck in fluid and around the drive motor fluid pump 204 into the downstream cooling and lubrication system by sucking cold oil in at the same time. This cold oil will be heated up subsequently, which will raise the fluid temperature even faster to continue with the waste heat mode.

jallred | 27 januari 2020

Wow! That's a lot of power. How many kW does it take to heat the large motor that fast? -fish

Actually, it would be energy. And your implication of the motor being large requiring even more energy, is a bit off base. They use the motor to create heat, but that doesn't mean the heat the entire motor. They actually focus on just some small components of the motor, mainly the end-windings.

In waste heat mode, the stator of the electric motor is powered to heat end-windings of the stator (and other portions of the stator 331 as well as the rotor 303) with or without causing the rotor 303 of the electric motor to rotate (step 706). Stator 331 powering without rotor 303 rotation may be accomplished by applying DC voltage/current to the stator windings by the stator drive electronics. Alternately, stator 331 powering without rotor 303 rotation may be accomplished by applying the same AC drive signal to each of the phases of the stator windings. Note that limited rotor 303 rotation may be accomplished by the stator 331 operating inefficiently to cause the rotor 303 to generate heat while rotating. The drive motor fluid pump 204 is then operated to pump fluid into the hollow cylindrical body 308 of the rotor 303 (step 708). Such pumping continues until the hollow cylindrical body 308 is at least substantially filled. By continuing pumping until the hollow cylindrical body 308 is filled, fluid exits the hollow cylindrical body 308 via the fluid exit ports 326 and flows onto the stator end-windings 305, the stator lamination 304, and in the air gap between the rotor 303 and stator 331 where the fluid gathers heat from the contacted components (step 710). The oil distribution ring 602 may assist in directing the fluid onto the stator end-windings 305 and the stator lamination 304. The operation of step 710 may result in the case 302 of the electric motor being at least substantially filled with fluid. The heated fluid is then pumped to heat exchanger 210 to heat coolant circulating therethrough (step 712). The heated coolant is then circulated via the coolant tubes 214 to heat the battery 106 (step 714).

jallred | 27 januari 2020


I also found this where NREL developed a Matlab toolset specifically for EV thermal management modeling.

andy.connor.e | 27 januari 2020

that was a pretty damn good explanation @jallred

jallred | 27 januari 2020

Yeah, they have to explain it well to get the patent. FISH keeps saying it would be "interesting to ask a Tesla engineer...". He doesn't realize that when engineers patent stuff they explain it in detail. Or they write papers about it in research journals. This way we don't have to "hunt" down an engineer. Patents, research papers, data sheets, applications notes... these are the ways that we communicate. But not so much through youtube bloggers.