Low ambient temperatures (Working and Storage): Question for Simon Hackett, page-5

If its like the Zinc Bromide solution from ICL for instance, which is 75% Zinc Bromide in water and is described as 'Battery Grade', the freezing point is about -8 Degrees C. Just googled for it.
Here is the product sheet: https://eif-wiki.feit.uts.edu.au/_media/technical:renewables:zinc_bromide.pdf
Don't know if its the specific one that Redflow uses but I imagine it must have similar properties.
If it expands anything like water does when freezing, I would guess that would cause a deal of damage!