Put it on a block of wood to keep it off the concrete. Or put it on a table or something like that.
It won't freeze, a charged battery doesn't freeze. If that were the case then you would have a frozen battery in your car daily during the winter.
Charge it... Then take the charger off. Check the voltage occasionally.
Hopefully you have that voltmeter of yours figured out by now.
If your reading over 15.5 volts on your battery while it is charging, something isn't right.
I don't think a smart charger would even put out over 15.5 volts while in a desulfation mode.
Check what the voltage is on the battery without the charger and report back.
2016 North Point 341RLTS
2012 F-350 Lariat CC SRW