...or just make it easy on yourself and keep the batteries in the rig over the winter. Just make sure your battery disconnect switch is 'on', isolating your batteries from any parasitic draw. Fully charged batteries will not freeze. I've left my batteries in our fiver over the winter for several years and have not had a problem. And it frequently gets well below zero here in northern Indiana. Just make sure they have a full charge when you 'put it to bed'.