get a test light, turn the vehicle off, test all the fuses for power on the side that should not be powered. Found a parasitic drain in my civic this way, ended up just pulling the fuse since the power locks didn't work anyways.
Also, cold weather is hell on batteries, drive the shit out of it and make sure that's its really charged nicely.
http://www.wikihow.com/Find-a-Parasitic-Battery-Drain <- that way uses a multimeter. I did it with a test light.