Speaking from experience if the weather is sub-zero and the battery is in any way weak then the cold will nail it. Where I am it gets down to -22 on a cold day and I've changed multiple batteries which in the Autumn were okay.
As others posters have said, it is probably time to get a new battery.
No harm to check connections at the poles first, but a 4 year old battery is past its best.
Isn't it a truisim really. Any battery thats not new is past its best. They get worse with age I assume?
Obviously though they may still deliver and retain enough current to start a car for a long time. I think one of mine lasted 8 or 9 yrs. I think the average is about 5 yrs though. Depends how its used and how hot and cold it is.