Yes, you can leave the battery installed, regardless of temperature. With heated storage, there is no chance of the battery freezing, but I would check the voltage a couple times over the winter to ensure it is up to snuff.
2017 Escape 5.0 TA (someday soon, I hope
2015 Ford F150 Lariat 3.5L EcoBoost
2009 Escape 19 (previous)
“Most folks are about as happy as they make up their minds to be.” — Abraham Lincoln