the older a battery is the less it likes the cold. the colder it gets in winter the more chance there is of a battery failing to start a car on a cold morning.
there are a few ways of dealing with a battery that is failing to start a car.
1. buy a new battery and find someone who recycles old batterys and give them the dying battery.
2. I'm not sure of what the product is called but it is basically concentrated battery acid in a small bottle use as per the directions on the bottle.
3. A Fujifan suggested check all the connections to the battery and make sure they are clean and tight. remove each connector from the terminal and clean the connector and the terminal. then when you get the car to run check that the alternator is doing its job.
finally if you are a bush mechanic

take the battery out of the car and give it a good side to side shake, not up and down as this can make acid come out of the vents in the top of the battery. this is meant to mix up the acid in the battery, get the scale off the plates in the cells and make the battery work better. (It does work Ive done it a few times)
TOONGA