> I have a 04 Prius
Then there shouldn't be any concern about the 12-volt auxillary battery (and there never is about the big battery-pack)... as long as the temperature isn't around 0 F degrees that entire time... and you remember to disable SE/SS.
The battery in the 2004 is bigger than in the classic. That really helps.
The catch is the SE/SS sensor is a new drain on that 12-volt auxillary battery. But no one has any real experience with that yet. So sometime before you leave, make sure to press the disable button on the dashboard underneath the steering-wheel.