2003 STS - No start

Okay, so last Tuesday I went out to start my car at about 10 AM. It was considerably cold (about 31°F) and when i turned the key my car wouldn't start.... All I got was multiple rapid clicks and the headlights were flickering along with the clicks. The clicks were in about a 8-10 click sequence. And it would last maybe 3 seconds. Even if I turned the key in the off position. So I went and jumped it from the under the hood positive terminal thing. And it started right up. After that it ran fine. Until today. (5 days later) I went out with my girlfriend to grab some food about 4 miles from her house....When I came back, the car wouldn't start. It did the same exact thing. It would click rapidly and the lights would flicker with the clicks...... The weird thing is that every electrical thing worked. (Windows, radio, dic, inside lights, headlights, etc). After turning all electrical thing off, I tried starting it again and it still just clicked. I checked the battery voltage on the DIC and it read "9.4 ok"...now that seemed extremely low to me, because I thought it was supposed to be at about 12.4. Anyway. We called my girlfriends mom, and she came and I jumped my car and again it started right up. Now here is my question. If the battery was bad, wouldn't the car not even have the ability to power any of the lights or radio? And wouldn't the car not even click? So what could it be if its not the battery. And how can I find the source of the problem?

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Oh today when it didn't start it was also 28°F. I don't know if that has any relevance