Car battery wont stay charged - 1993 Buick Roadmaster

If the battery is more then 5 years old .. replace it
The cold weather will cause a seemingly good battery start to fail.

You most likely have a bad battery,or the alternator is not charging correctly,it should read at the battery 13.65 volts to 14.25 volts with the engine running and everything on,lights blower on high etc.If it is not charging at least this,then replace the alternator,and slow charge the battery(2 amp) for about 24 hours.If the alternator checks out fine,then there is a draw .A draw is a 12 volt circuit that is on,while the ignition is off and the lights are off,and the doors are closed,nothing on.It can be a lot of different things,the alternator can check out fine,but still can draw ,if a diode is bad in the alternator.Un- plugging the alternator and checking for a draw is the only way to check it.