Ford flex wont start in cold

Ford flex 2013 will not start in cold weather 35 or below it did this last year took to a ford dealer they replaced and said it was the battery which we had already replaced brought it gome the next day the same thing. It started fine and ran fine everyday all spring and summer now the temp dropped around or below 35 and it will not start. It cranks over fine and only happens in the cold if it warms u to 50 or 60 degrees out it will start noone seems to know what the problem is.