You forgot to tel us how old the battery is. Maybe you can tell me if your parking the car in a garage or not. If not, what is the normal temperature outside?
Its pretty normal that this problem occures when its cold outside. Remember that you'r car is not able to charge a battery when its almost flat..
Check the acid level of the battery. If its too low, then find some water and fill it up. ( not to the top )
Then find a battery charger and let it charge the battery for 13-20 hours.
This should do it.
If not, then you need to buy a new battery. If your driving in cold weather, then make sure that your new battery has a high C.C.A ( cold cranking amps )
Chris., February 2012