It is my understanding they are insulated and heated/cooled as needed; the performance loss from being cold is much larger than the energy expenditure to heat the cells to an optimum temperature.

Around where I live, we have several weeks of -15C - -25C (5F - -13F) every winter. No worries for the EV owners, they just need to charge a bit more often as they need to heat the interior of the car, too... (Not being afforded the dubious luxury of simply utilizing the waste heat from the engine, as I do for the time being in my diesel...)

They’re usually actively heated/cooled