See the overkill manual for a decent explanation.
I only would suggest setting the low-temp to 5 celcius, and release at 7 or so.
At a low temp, you can't pull any amps into the battery, especially <5c. Below 0 charging should not happen at all.
Also take into account the location of the sensor. Usually, this is mounted on the cells. That doesn't give accurate readings for the actual cell core temperature. If you put the battery in a heated compartment, the sensor will read 0c pretty soon, since it's more affected by ambient temp, while the core of the cell is still much colder.
5c is, imho, a better option, since it does leave some marging for the cells to get a little warmer (More likely the core temp is also starting to - slightly- rise.
The better you can get the sensor to the core, the better. I've installed mine in a small gap in the insulation sheets between the cells - so it's barely affected by ambient temperature