I've got an 06 Dodge Ram with the diesel engine. My truck sat for a week once in sub zero overnight temperatures. When I tried to start it, it was -22 degrees.
I won't say it started easily, but start it did. Once it was running, it warmed up and ran as it always does.
If it were a concern, I'd get a good battery with lots of cold cranking amps and simply carry that. If I was worried about starting, I'd use the batteries in the truck to preheat the fuel and in coming air, then hook up the extra battery to backup the one in the truck.
Unless they have been really depleated, that should work. E
