I move the two head units of my Humminbirds to the house because I don't want to chance it-too much $$$ and too easy to do. The batteries stay hooked up to a digital onboard charger that goes into trickle mode after 21 days and I've never had a battery freeze on me.
2X Dutch. Battery Tenders over the winter, but then I have two Optima gell cells for my troller and they're pretty resilient.
Life has many choices, eternity has two...choose wisely. Unapplied biblical truth is like unapplied paint...how many gallons do you have sittin' around? U.D.