Frozen House Batteries

If you take them out to thaw, make sure you place them in a container so if the case is cracked you don't have battery acid leaking on to some thing you don't want it on.

Thaw them out, then charge them VERY SLOWLY with a trickle charger. If they are 6v's, charge them individually at the appropriate voltage. Will take several days. Then try them under load.

DO NOT subject them to your vehicles charging system or your rv's converter-charger. And no need to test them prior to charging. Obviously they're not anywhere near an acceptable state of charge for being put back into use. See how they handle being charged, first.

I might try bring them inside and let them warm to 70+ before putting a small charger on them. If they charge up and hold 12.6 volts for a few days put them back in the RV. Otherwise take them in for core exchange on a new set.

A fully charged battery will not freeze until you get to about 80 below zero.

I had two 6 volt house batteries in our 96 Southwind freeze about 4 years ago.
They were slushy, not frozen solid.
After being thawed and charged, I continued to use them. They're still in use but, will be replaced in the spring.
If the cases are not cracked, I would try to charge the batteries.
Maybe you will luck out.
As a result of the freezing, I keep the RV plugged in 24/7 when it's not in use.
I won't take that chance again.

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