[JFP in PA]

I think the issue is that the battery charging profile is temperature dependent, meaning that any given charge cycle profile has both upper and lower temperature limits where the current level and duration become less effective (batteries also can actually freeze if they get cold enough). The electronics in the unit itself are also temperature limited as well and may not function properly outside the stated range.

But the question has to be are both your battery and the Ctek unit going to see long duration time frames below -4F? We see negative temps where my shop is, and the inside temps of some unheated garages in the area are actually in the 20-30F range when the outside air temp is -5F. In these situations, the Ctek unit works fine.

If both the battery and the Ctek are going to see prolonged temps below its operating range, it is time to pull the battery and the Ctek and move them inside so they both will be happy…………… Otherwise, you are going to need some more specialized maintainer for very cold use.