Does charging in extreme cold accomplish anything?

Don't know if this will answer your question but around 3minutes in this gentleman explains the traction battery heater operation. If you doesn't answer your question you could probably contact him.

 

Our winter temp is never that cold, but I have had no problem charging my car in a few sub 0F (-18C) temp down to maybe -25C nights outside without any ill effects. But -30C daytime high is another story. There are a few warnings in the manual about operating the car under "extremely cold" (-30C and below) condition. It may not be possible to start the car under those temperatures. Do you keep your car in a garage where the temperature is higher than outside? Once you start the car, the cabin heat will bring the traction battery temperature to a safe operating range. If you have any charge in the traction battery, it should be able to run EV albeit very short.

 

Ed, I've read that at least one other PC member (besides myself) uses a space heater in the cabin during frigid temps to help keep the pack warm. I think he is in Alberta or Saskatchewan and also mentioned that for him locally, most if not all charge stations also provide a normal 120 volt outlet that can be used to power the space heater while charging.

If you chose to try the space heater while charging a couple of tips are:
find a 3 wire flat pigtail extension and cover about 2 feet of it with duct tape, than it can be safely placed under one of the back doors.
At home don't try plugging in both the EVSE and the space heater on the same 120 volt circuit.
Avoid plugging the space heater in while it is turned on, simply knock the space heater over so the safety switch turns it off before you plug it in or unplug it.
Adjustable heat and fan speed knobs are nice too, but not essential.

 

That battery-heater alone is reason to stay plugged in during "extreme" cold. For those who experience intense winters (for me, that's Minnesota), it means theplugged-supplied electricity can be used far more than you'd expect. Notice on the following video how, despite the outside temperature of -1°F (-18°C), the battery-pack is kept at 55°F (12°C). That means it can be taken advantage of still. Watch the % for the charge-level in the detail provided by the following video:

The coldest extended duration I have experienced without plugging in was Christmas 2017. We were out in Wyoming celebrating with family. Sitting there for over 8 hours in -9°F (-22°C) unassisted meant only minimal electricity from the battery-pack would be available. (Lithium chemistry experience a increase in resistance when its temperature drops below freezing, hence heating it for better draw & charge efficiency). The system started just fine. I obviously let it warm about for a few minutes before driving, but there was nothing else special needed... only some patience.

For those who experience ordinary winter, the battery-heater means you'll be able to squeeze out as much electricity efficiency as possible. You still driving in full EV mode until the entire EV capacity is depleted, as this video shows in detail:

 

See my discussion of that passage and a follow-up posting in a previous thread.

 

For temperature below -30C, as discussed above, it may be beneficial to keep the car plugged in to keep the battery heater function. As for the usefulness of the battery charge is that if your price of electricity is not high, no matter how short the EV range is, you can get more miles on pure EV. In my case, our electricity rate is very high. Currently, EV drive on wall charge costs just about the same or little bit more than running my car on HV using gas. For this reason, I did not charge my car for the entire month of Feb last winter. But after that month, I started again charging my car, just so that I can reduce the use of gas for my commuting even though I know it was costing me more to charge and run the car on EV. So, it is up to you, if the battery heater function is not needed, you can leave the car uncharged and keep driving HV. But if you have any chance to charge your car cheap, there is nothing to lose, except a bit of inconvenience as you have described.

 

1. It automatically turns on when the battery temperature drops to around freezing and turns off when the battery reaches a few degrees above freezing, as long as it's plugged in. Apparently that continues for 3 days, but it's not clear what happens between days 3-31 if you have a Canadian model.
2. I have no idea how the charge timer affects the traction battery heater, but maybe they mean that it pre-warms the battery before it charges?
3. I have no idea what this means.

I've seen the traction battery heater run when it's only moderately cold. Sometimes when I unplug my car in the morning the green charging light is on, even though it's fully charged, which means the traction battery heater is running. I would definitely suggest plugging it in whenever possible, since the hybrid system can work most efficiently when the battery is above freezing. For example if the battery is too cold, regenerative braking will be severely limited, so you'll lose efficiency from that.

I've noticed that the battery retains heat fairly well. It is often still 10 degrees F above the overnight low temperature if I park it without plugging in overnight, if I drove it the day before. If you drive everyday and plug in every night, I don't think the battery will get too cold. Also note that inanimate objects don't care about wind chill. The battery won't get colder than the actual air temperature.

If you want to do a block heater and plug in, you could set the car to limit charging to 8A. That plus a 400W block heater is under 12A, so OK for one 15A circuit.