Seems the auto focus is more related to background than cold. I have a 7D and it is not real fond of red against green on water. They all work on grayscale and some cameras do a better job of handling it than others, but they all have little quirks about color. Seems to me if you are shooting anything other than sunny days you may have that problem.
Mine seems to throw a fit on a hazy overcast day when it acts up, hot or cold. Take it outside in the snow from the house on a really gloomy day and try focusing on a like colors in the foreground and background and it just hunts from infinity to minimum focus, my 60D does the same thing. Just not enough contrast to focus on.
If you are using batteries that are few years old replace them, LiOn batteries do not like the cold anyway. As they get old like some of us they just have less energy. The mind/battery is willing but just wants to be in by the warm stove.
If they make a dual battery grip for your body that will help. You will get a little better than double the shots as the voltage stays up longer before it starts to tail off. I get over 1400 shots at 90 degrees with 2 batteries with my finger on the button all day long instead of the 500-600 on one battery. It never fails, the shot you really want is wasted on a battery change.
Use of faster memory cards also reduces battery loads as the camera does not spend as much time downloading them to the card. They get a little slower in the cold also. Really, what is it about age and cold anyway???
If you are using the preview screen in the winter it is just sucking the life out of your battery. It is bad enough in the summer time. That little screen is the battery demon incarnate, turn it off in cold weather.
Dave Fox