That hasn't been my experience charging outside in the northwest with average winter temperatures. But the charger does power a heater to keep the batteries ar

That hasn't been my experience charging outside in the northwest with average winter temperatures. But the charger does power a heater to keep the batteries around freezing, so you're right, it's better to charge in a garage. And cold weather causes additional losses, but I would expect no more than 20% or so. I lose 10% range just by running the dashboard heater.