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I own a 2018 M3 RWD and the following is some information I gathered using SMT.

With the car not plugged and the ambient temp around 48F the car draws 3.5KW to heat the traction battery and about 7KW max to heat the cabin for a max total of 10-11KW. When the car is plugged into my [email protected] it supplies 5+KW of the 11KW. The only option I found that would heat the cabin and NOT heat the traction battery, via the traction motor, was camping mode. I did not run the test for very long so I am not sure at what cell temp the battery heating would terminate? I do know that when actively charging the battery heating to accept a 22mph charge rate stops at around 54F. I think heating the traction battery while heating the cabin is new? I can see times where heating the cabin and NOT heating the traction battery might be my preferred option and the only way to do so is using CAMP mode.

I also monitored the rear motor power, motor torque and brake variables and it appears to regen down to a complete stop, which surprised me, and then after about a second the brake is applied. These reading were observed while set to the single pedal driving mode.
 
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Yep. This happened to me when the battery was cold. It couldn't accept regen but by doing some regen and at the same time working with the other engine you get some regen anyway plus you heat the battery. It's not wasteful, it's regen braking energy you would not have had otherwise because the battery is too cold to accept it. I think it's pretty bright.
 
Yep. This happened to me when the battery was cold. It couldn't accept regen but by doing some regen and at the same time working with the other engine you get some regen anyway plus you heat the battery. It's not wasteful, it's regen braking energy you would not have had otherwise because the battery is too cold to accept it. I think it's pretty bright.

That's an interesting concept if its true.

I will have to think about that. hmmm using one motor against the other to produce regen. hmmmm
 
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Yep. This happened to me when the battery was cold. It couldn't accept regen but by doing some regen and at the same time working with the other engine you get some regen anyway plus you heat the battery. It's not wasteful, it's regen braking energy you would not have had otherwise because the battery is too cold to accept it. I think it's pretty bright.

Yes, I can confirm. The front motor on my P3D+ does indeed heat the battery pack during pre-conditioning. It generates 2k to 3k of current. The most amazing part is one that I can't understand - which is....its always in regen. It got the battery pack up to 88 degrees F ( from 62F ) before I reached the supercharger.

Also interesting is that the battery pack never stopped heating up during chagrining. The battery pack reached over 125F during charging which leads my to my next question. <----The front stator reached over 210F and its oil temp reached 180F at that time.

What is the optimum battery temp for charging? Anyone know.

How does a single motor Model 3 pre-heat the battery pack? Anyone know?
 
Optimum battery temp seems to depend on the amount of energy you're trying to push into it at once. Slow charging at home seems happy over 10C, supercharging needs a higher temp. 50C seems about right, and that's around the 125F you're seeing. I'm sure someone posted those temps somewhere, I don't have them handy.
Preconditioning the car interior also heats the battery using the engines as you say. Even without preconditioning the interior, the motors will be used to heat the battery if you are trying to charge. Preconditioning en route to supercharger works in a similar way, albeit with a high temp target.
The single motor Model 3 will simply heat a bit slower, having just one engine to generate heat instead of two. I'm unsure how it's able to preheat while driving to a supercharger. I'll guess the heat produced from normal driving gets used but it must be a slow heating...
 

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