If you are able to barely able to get your battery above zero degrees C, that doesn't mean it can now accept maximum charge rate.
A posting earlier in this thread has tables from some manufacturers showing that the acceptable charge rate is about 0.1C, for a battery which can take 1C at moderate temperatures.
...I glazed over...Soooo far past me...... but, does this mean that the claims of the -20F chargeable LiFePO4 cells could be true? Based on what i’ve read in this forum, not for any practical use. I’m no expert on the matter, though.
diysolarforum.com
What that doesn't mention is the voltage required to put in such current.
Upnorthandpersonal's comment is that at normal charging voltages, very little current flowed at -20C.
It is possible the manufacturer's table showed currents that couldn't be achieved with a voltage-regulated charger. But without knowing that for sure, I think you should limit charge current according to those tables.
If you're using a separate battery charger for emergency charging in cold weather, better limit it to 0.1C (or 1/10th of whatever maximum C rate battery is specified for) when just above freezing.
For your system's PV charger, I would determine the C rate it was capable of delivering, then adjust low-temperature cutout to a temperature where that C rate is allowed. Perhaps > 7 degrees C for 0.3C charge rate, using the ETC table.
If you have multiple charge controllers, one could have zero degree cutout and the others higher, for a stepped charge rate vs. temperature.
Not an issue of PV wattage is less than 1/10th battery Wh capacity, which would provide max 0.1C. But something to consider for larger PV array.
What we really want is for battery charger to have temperature compensated charge rates.