An old deep freeze is probably not sufficient, but packing them into a thick layer of insulation should be fine for the winter. The insulation would have to com

An old deep freeze is probably not sufficient, but packing them into a thick layer of insulation should be fine for the winter. The insulation would have to completely enclose them though, including the bottom. Maybe best to have them sit on a thick layer of insulation on the bottom, and a box that can be removed during the summer months so the batteries don't overheat. Another a bit weird idea would be to somehow put them next to a compost heap, which produces low temperature heat for a long time (years) including during the winter.