I have trickle chargers on my two vehicles that don't get driven very often. Also have chargers on my two tractors to keep them ready to go at a moments notice. It's really a smart thing to do to keep batteries from prematurely going bad, it can even extend their life past the normal time period.
Not to mention that as the charge gets lower on the battery the freezing point goes up. A discharged battery will freeze solid at 32*F, but one that's fully charged won't freeze until about -76*F.
The longest my truck has ever sat was about 35 days. It was not cold, it was during the summer. And I had my alarm armed the entire time. It started right up when I went to move it out of the yard. Now my old Cutlass on the other hand would go dead after about 3 weeks if I had the alarm armed. But when it was stored in my garage I didn't arm the alarm and the battery lasted much longer.
