Leaving the battery in an unheated garage in styrofoam containers will not keep it warm. Insulation only keeps things warm when there is a source of heat that is producing at least as much heat as the insulation is allowing to pass through it.
The advice to electric car owners is to not recharge in your garage. I've seen nothing about just parking in your garage.
I've taken the same attitude with my bike battery.
Now, full disclosure, I don't own an electric car.
I think best practice is to store at 60-70% and in warmer room for the battery.
With the beautiful Easter weather today in western NY, I decided to ”unwinterize“ the ebike and take it out for a ride later this afternoon for its first spring voyage. Got the brake discs wiped down with alcohol, tires inflated to 40 psi, dust from the garage cleaned off, chain lubed, and charging up the battery and my extra tail light.
Here is my last battery charge check of the off-season, which still shows a blue charge.
View attachment 8322
So after almost 5 months of storage in its protective bag, kept at room temperature (we’re usually around 70), the battery never dropped below 80% charge (impressive, as that’s about where it was at when I stored it).