I have four, old 12V marine-type 100 AH batteries I bought from Walmart 10 years ago that amazingly seem to still be serviceable. They've been stored in the heated garage for the past four years, and I periodically recharge them 2-3 x/ year. I even used them to power my solar setup for a few weeks about 12-16 months ago, until my LFP batteries arrived, and they performed well. I'd now like to put them in a small, enclosed trailer at a remote property we own, to power a weather station and mobile hotspot (that will allow the weather station to report). The big worry is that the trailer will have no heat, and outdoor temps can get to about -15F for a night or two each year, with temps in the single digits common. Will be charging via solar (still need to calculate that, but not worried about that aspect). Total power consumption will be very low, with a continuous draw of only about 20-50W, depending on whether or not I also add a camera. My big question is, do I need to worry about these batteries freezing, or can I just put 'em out there and let 'em do their thing? I've never used marine batteries in such a cold environment. I really just need to get about 6-10 months of use out of them, until a building we're putting out there next year is ready.