I've lived in Minnesota all my life and have never had cold kill a battery. What WILL kill your battery is low/no charge or over-charge. Low/No charge will kill your battery; and this where cold can be a problem as the battery can then freeze. Conversely, over-charge can happen unless you have a smart charger. IMO, a typical 3-stage RV converter/charger is not a smart charger. It does reduce to a trickle charge. But that will over-charge your battery ultimately; or at least "boil" water out of the battery.
So, bottom line, you can leave your battery in the garage. I would put a Battery Minder or Battery Tender on it. They are smart chargers that will keep your battery in tiptop condition and also will use anti-sulfation technology to treat your battery. I got 10 years out of my motorcycle battery using this type of product. I also use one on my Trojan deep cycle RV battery. It sits in my barn, in the cold, all winter. It's always ready to go in the spring and will last for years.
2012 F150 FX4 Ecoboost, 2016 Surveyor 274BHS
2003 Yamaha FJR1300, Demco Premiere Slider
1969 John Deere 1020, 1940 Ford 9N, 1948 Ford 8N
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