If your charger is a smart mode charger it probably will never heat the batteries up enough to boil fluids out. I lost one battery due to the fluids being boiled out and then changed over to smart mode charging. I still check my batteries every couple of weeks but never see them low on fluids any more.
I probably would just just remove the batteries in your case since you are not around to check on them for that long of a time frame...
A fully charged battery will not freeze but being disconnected for that long of time the charge would probably start dropping off on you unless you had some sort of solar trickle charge feeding them.
Batteries are too expensive to just abandon for that long of time without hands on maintenance of some sort.
Roy Ken
