Ok, it was cold this week but that shouldn't knock a good battery over. If you didn't give it much chance when you drove home from the station, headlights, heater on etc then it wouldn't have recovered from that hence the flat battery again this morning. It's on the way out I should think, take it in to a local garage and have them put a battery tester across it if you like but if it were me I'd buy a new one and be done with, assuming your alternator is charging correctly of course. If your battery is weak then the cold weather wil always find it out. Hope this helps.