Ahhh, my favourite topic.
tl;dr version: Battery get hot. Very hot. Battery stay hot. Much waste. Confusion. Anger. Acceptance.
Many, including my past self, have preconceived notions of how the battery temperature management must work. Many, including my past self, are apparently wrong.
I too assumed all these noises and fuss were from cooling, and I was very wrong (see:
Time Remaining vs. kW rate and also
Battery Cooling: How Important?). I ain't got no high horse to ride here, but I do have new knowledge to share!
The first thing to know is Tesla seems to treat all DC charging the same, whether it be from a Supercharger or a CHAdeMO station. I'll explain why this is bad later.
Charging Basics
Lithium ion batteries, like those in our car, can be safely charged faster at lower states of charge (SoC). At higher SoC, they must taper off. In general, too much heat is bad, but Tesla has found it is beneficial for charge speed (not necessarily health).
Preconditioning Prior to Supercharger Arrival
Precondition temperature targets are
variable. The goal is to raise the battery temperature by wasting heat in the drive motors, which heats the battery, which allows for a faster charge rate. The AWD is potentially better than the RWD at this, since it can fully use the front motor for heating.
Generally, at low SoC, the target heating temperature is also relatively low, perhaps 30°C. The battery may very well be above this already and preconditioning might not be needed, especially if you have leftover heat from the last Supercharger (uhh, spoiler warning).
At high SoC, it gets hotter prior to charger arrival. I don't recall an exact number here (it's not often I stop to charge at high SoC since it's so slow), but it's definitely significantly warmer. Perhaps 43°C? Maybe a bit higher? Completely depends on SoC though.
Conclusion: My
theory for this behaviour is that it needs more heat to pump the power in at higher SoC. Why? No idea, really. But at low SoC the battery can already accept much, much more power than high SoC and maybe needs less "help" from active heating to achieve high charge rates. Additionally, low SoC implies it has more time during charging to continue to heat the battery anyways.
During Charging
This sucker's gonna get even hotter now!
Charging induces quite a lot of heat. Most people think you want to get rid of this heat. Hah! Tesla laughs in your face.
100% confirmed, the battery will continue to be actively heated with the drive motors while DC fast charging,
in addition to the heat added via charging at such high powers. And it will continue for a LONG TIME.
The drive unit internals get super hot. Apparently like 100°C hot. This is to heat the battery, again. Which gets super hot. Like hurts-to-touch hot. I want to say it can definitely get as high as 55°C. While heating, the motors will be hotter than the coolant, and the coolant will always be hotter than the battery. Yes, the "coolant" is actually being used to heat the battery. Terminology is confusing.
The technicals: 3.5kW/motor is what we've seen. This seems
about right but I have some more precise data coming soon (I expect it's a bit higher or I have some unaccounted-for electrons). The "most efficient" Model 3 would probably then be the Long Range RWD (not AWD), since it can waste less heat during the charge compared to its charge rate.
Cooling may or may not occur during your charge (especially based on my SoC theory above). I'd almost bet money that if you stop before 90%, it probably will still be heating.
Conclusion: Your motors and battery will be rippin' hot during charge, and cooling may not occur until the very end of your charge,
or...
After your charge
Cooling begins! The radiator fan kicks in (yes, a Model 3 has a radiator, it's even in the usual spot for cars), and the AC
may kick in depending on parameters I appear to have no understanding of. Anywho, it doesn't cool that much. This takes a few minutes, much less time than the heating takes.
Many minutes down the road, you will notice your battery is still at something like 35°C. This is apparently normal. Both in the cool of Colorado in March and in the hot summer of my home area, this seems true. It's like a happy temperature for the battery to stay at; it could easily cool it further in Winter with the radiator alone, but it just... doesn't.
35°C sounds too warm. Everything we know about phone batteries says this is too warm, and the Model 3 battery pack is different from those in
size more than anything else. Many praise Tesla for their thermal management, but few seem to know just how hot the battery pack usually is.
Conclusion: Your battery will stay quite warm after a charge, and battery cooling is fairly minimal.
Extra benefits of a hot-off-the-charger battery
Well, you can coast into the next Supercharging without it needing to waste as much to heat. For Winter road trips this is kind of a good feature? I'm not sold.
But where this is sweet for Winter is actually with the Model Y and cabin heating. It's just using the 1000lb battery as a massive thermal tank with a heat pump, unlike the Model 3 (which uses a resistive eletrical heater for the cabin). Having a hot battery means it can draw heat from it for quite a while for heating the cabin before resorting to less efficient methods (which are nearly equivalent to the Model 3 heater).
Conclusion: Hot-after-charge batteries are actually useful in the context of Winter road trips (where you're likely using fast charging the most). Summer? Not so much...
Implications for CHAdeMO Charging
This sucks for CHAdeMO charging. I've sat at CHAdeMO stations for an hour and it heats the battery the whole time. Keep in mind it's not preconditioned prior to arrival for CHAdeMO, there's just no way to do this.
25kW CHAdeMO chargers exist around me. 50kW ones are more common, but sometimes 25kW is what you have to use. In another case, I had access to only a 10kW one or a 6kW Level 2 charger.
The 6kW Level 2 charger is faster for Model 3.
Why is that? The car decides to take a decent chunk of the available power for heating the battery
because it's DC charging. Basically, they have the assumption that all DC charging will require maximum throughput. This is great for the Supercharger network, but absolutely not necessary for CHAdeMO charging,
especially lower-powered ones.
For Level 2 AC charging, it behaves entirely different. It only gets the battery up to about 15°C (I can't remember, somewhere in my post history) even for an 11.5kW setup. So
Tesla is basing the target temperature on the type of charging, not the communicated available charge power.
Even at a 50kW station, something near 18% of the station's power output is getting completely wasted. The battery is almost certainly hot enough (I've charged at Superchargers when the battery is cold, so I have an idea of what it
can pull at lower temps). If anything, only
brief heating might be necessary to increase throughput. Don't get me started on the 25kW station math. It makes Model 3 one of the worst rural BC EVs - it has the range, but the charging sucks. Yes, other EVs handle this better.
To make matters worse,
the car lies to you in the unit most people understand: Time. The 10kW station made this the most obvious. Tesla does the time calculation for DC fast charging based on powered received from the station, not power that will actually make it to the batteries. Normally this is close to rounding error for a Supercharger, but it makes a significant difference when nearly 20%
at minimum is being wasted at a CHAdeMO stall.
Conclusion: Tesla Model 3 is the most wasteful and slowest-to-charge EV if you must use CHAdeMO stations (like in BC, Canada). I don't see them fixing this uncommon case because frankly, I don't think they care about the consequences.
"camalaio's take"
I do think it's an excessive waste in some cases as well. In Winter I definitely appreciate the preconditioning, because it is
very slow otherwise. But I'd really like the option to, say, add 20% to my charge time if it means wasting less energy and/or having a cooler battery.
Thinking about this for California makes me a little sad. So many Teslas there using Supercharging as their primary charge method. It's a lot of waste and a lot of thermal cycling.
As the industry moves towards faster charging standards, bowing to consumer desires, I don't see this getting "better". Tesla probably doesn't give you the option to slow down Supercharging, because that implies you effectively tell the next person in line they need to wait longer because you care about your precious battery and/or waste like it's more important than where that person needs to go in a timely manner. Early adopters adapted to slowing down in general since they need to stop and charge. Common adoption will require the fastest charges possible.
The singular exception to all this hot battery stuff is Track Mode. I've yet to get my hands on one to measure what it does, but Track mode will actively and preemptively engage battery/motor cooling to my understanding. This is an interesting contrast to the Model S/X Ludicrous mode, which apparently heats the battery so that they can achieve higher discharge rates (just like heat is used to raise charge rates). The implied difference is launch (short duration) vs. laps (long duration).
Actual tl;dr: Yes, the battery is heated quite a lot and this is normal for a Model 3. Cooling is quite rare and very brief, and still leaves the battery objectively warm. Model 3s run a lot hotter than many people think, and the temperature is more passively managed than many people expect. It took a lot of measuring, reading, and being wrong to determine this.