Should I replace my car battery?

Should I replace my car battery? - 1
Added (1). I have a 2007 Ford Five Hundred. It hasn't been used much over the holiday period - it was probably last driven on 12/23. Not sure how old the battery is but I don't think it's been replaced for at least 3 years.
Added (2). When I tried to start it this morning, it make a fast clack-clack-clack-clack sound and wouldn't start. Now it's not even making the clacking sound. I tested the battery with a multimeter. It came up with a reading of 10V the first time. I tried it again half an hour later and got 8V. That time, I also tried turning on the headlights to see if that would move the needle at all. I think it did but it wasn't significant. Should i replace it?

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