It depends on its state of charge, and is one compelling reason to use a battery maintainer in the winter.
A fully charged battery is good to -76F / -60C, but a fully discharged battery will freeze at 32F / 0C, just like water.
I haven't seen data, but freeze temperature for a partially charged battery is probably roughly linear between those two points.
When a battery freezes it usually ends up with a cracked case, leaving a pool of acid underneath it.
Sky NA 2007 Midnight Blue
Sky RL 2008 Carbon Flash - Naked