Wow that's crazy...glad it isn't too bad.
Since I moved to the East Coast, I haven't gotten a car yet, but this cold temperature battery thing was on my mind. In NJ/NY we don't have it as bad as Vermont but cranking my rental car at 0F on Monday was pretty unsettling...it sounded like trying to crank the car with a dead battery.
This company builds batteries with heaters in them (heaters activate when the battery is "being charged" but too cold to actually charge), but the cells are not the high current type that you would want for a car starter battery unless you have a really, really tiny engine. I suppose they're a good candidate for pairing with capacitors but that's some extra hassle.
https://relionbattery.com/blog/lithi...y-cold-weather
As you can see, the RB-35X is 35Ah but can only charge at 2C (70A) and discharge cutoff is at a pretty weak 160A. On an older car with a 90A alternator and a small 4 cylinder this is probably fine, but anything newer usually comes with a more powerful alternator that could potentially fry the battery.
I think a DIY heater to emulate this on a higher current capable battery could work well. Have a diode preventing current from flowing to the battery, and a relay to short that out at 0C, then have the heater connected to the alternator and have the same relay shut it off simultaneously.