Cranking the engine in cold weather takes more effort from the batteries so could be a sign that one of your batteries is weak - I would get a tester on your batteries to check condition. I had same problem in cold weather and one of my 2 batteries had seen better days. I've also got an isolator fitted to prevent and draw from the batteries when parked up for long periods - my DAF 45 is a Horsebox.
Craig, January 2013