This is interesting. I wonder if large capacitors could alleviate this: somewhere to quickly dump the regen energy, and charge the battery with it at some slow rate equivalent to the long-term average regen load. Not only would it help in cold situations where the battery can't be charged quickly, but also situations where the battery would be healthier if not charged quickly, which is always.
Are you sure this is related to the cold, and not just that the batteries were fully charged so that regen had nowhere to put the energy?
[Edited to add]: I say this because I see this in all types of weather: I live on the top of a hill, and if the car is fully charge there will be no regenerative braking when heading down the hill.
Contrary to the knee jerk reaction some people seem to be having, this isn't an conspiratorial attempt to pull the wool over the eyes of Real Americans(TM).
I don't understand the reaction, anyway - ICE vehicles plunge in range with cold temperatures too, and there are a bunch of reasons why EVs seem well-suited to rural life.
The range reduction doesn't mean squat when the longest average commute in the US - Maine - is 10 miles. Who cares if your 300-350 mile EV only gets 200 miles, when that's still 20 days of commuting, and every hour your car is in your garage, it's "gassing up" with no intervention on your part beyond a few seconds to plug in a cord when you get home?
FYI, looking at a smattering of temperature charts, "much colder than 20 degrees for extended periods" is a slight exaggeration for Minnesota.
Regardless, I agree there’s still good use cases for EVs in cold climates.