[hayden55]

Chiming in have you considered rigging up an adquate bms and an electric blanket to mimick the stock battery on the ioniq? Lithiums aren't ever supposed to charge below freezing so you would have to design a circuit to turn off charging until battery temps above 32F or maybe even warm it to optimal temp around 60-70F then shut off your blanket, and the charging and discharging should keep it warm. Then at that point just have a thermal switch turn on and off a fan.
Also,
18650 batteries used are also a much much better option. Life cycles are so long, second life 18650 usually have like 95% life left.
It would also weigh like 3-5 pounds to it wouldnt take much to heat and cool.
I bought some LG1 3350mAh cells for a m12 milwaukee heated jacket. 1 pound. 12.6V charged at 10.05Ah (9 celll pack) has the same capacity as more than three of the oem m12 batteries. They pack a punch for their size.