Pretty sure the ones in most EVs today work fine at -10C, but they may lose some efficiency. The thing is, there's already mechanisms in some cars to generate waste heat specifically for this purpose. Tesla's already have the ability to run their motors 'inefficiently' generating waste heat, which can be pumped into the battery coolant and heat that. It's no better than electric strip heating, but it doesn't add any cost to the system.

The real benefit, in my view, to being able to charge at cold temps is to improve overall efficiency. If you have to waste some amount of power to heat the battery then that is power that could have been used to charge the car instead...