And by mumify, you mean wrap them in insulation for the winter?
Insulation really does make a big difference on lead-acid batteries.
I also have a section of heat tape below my batteries, but I don't use that until it gets really cold out.
Also, having a car to park the car in is nice as well. My friend Tom has an electric car AND a HEATED garage.
I am jealous of his garage. It is cozy in there.