if those batteries are not fully-charged, they can freeze at warmer temperatures. Due to the nature of their design, flooded batteries can also freeze at warmer temperatures, especially if they are not fully-charged. When a battery is not fully-charged, the sulfuric acid and distilled water inside the battery are not properly-mixed and the distilled water can freeze.
If this happens, a battery could be damaged and may need to be replaced. If your car has sat in very cold temperatures for an extended period of time and won't even turn on dashboard lights, your battery may be frozen. DO NOT ATTEMPT TO JUMP-START OR CHARGE A BATTERY THAT MAY BE FROZEN!
The first thing you should do if you believe your battery may be frozen is visually inspect the case. If you see cracks in the case, the battery may be damaged beyond repair and should be taken to a battery retailer for inspection and replacement, if needed. If the case appears undamaged, move the battery to a warmer, safe location, where it will have an opportunity to thaw out on it's own. Do not attempt to accelerate this process with artificial means of any kind.
Once the battery has been thawed out, you can check it by re-installing it in your vehicle. If the dashboard lights or other electrical accessories still do not function, take the battery to a battery professional and have them inspect and test the battery. If your battery is able to start your vehicle, there's a good chance it is still significantly discharged. After you have verified that it can start your vehicle, we recommend fully-charging your battery to at least 12.6 volts, depending on the type of battery you have.
- See more at: http://www.optimabatteries.com/en-us/experience/power-source/what-happens-if-my-car-battery-freezes/#sthash.spPkzk5A.dpuf
