Hi there Jack!
I personally always believe in removing the batteries if a long period of non-activity is anticipated.
Depending on the type off cells involved, one can never guarantee that some 'gassing' or other chemical process may cause corrosion on the metallic terminals, etc. So "Better safe than sorry." as the old saying goes.
If you have an old spare woolen sock, then pulling that over the control box is another good measure.
Keep the machine in a warm place, avoiding any moist air locations. (Wrap the control box it in a dry cloth to act as an absorber, and check its 'dryness' periodically.)
So you have a great Christmas, and let's hope 2011 brings you warm days and good hunting with your EXT.
p.s. Here in the UK the present cold spell shows as 20 F at night, and about 4 F during the day.
Maybe I'll get some quality time in on the local beaches....TheMarshall.