Your Civ was made in 2007?
So, you've got an almost 7 years old battery.
I think, you should definitely have a new one.
I bet, you won't regret it.
But even with the best battery you can ever find, you shouldn't leave your Civ undriven for more than three weeks.
That's even more true for the cold season we have right now.
The Civ, just like many cars nowadays, is sort of a "mobile computer" with tons of electronics in it, and all of these features want to have enough power in order to work, which is hard to provide for a battery, a device which, unlike the rest of a car, has been technically almost the same for the last few decades, actually.
Besides of this, the available space in the engine bay is very limited in the Civ. So, depending on your model, it's quite difficult to fit another battery with a higher capacity.
Some of the users here on Civinfo seem to have managed to fit the battery of the diesel model by using another battery holder.
As far as I remember, this would give you 71Ah instead of the 45Ah of your petrol model.
Don't know whether or not this might be an option for you as well.
Oh, and let me this:
Just in case you want to try to replace your battery by yourself:
leave your key in the ignition lock during this procedure.
Otherwise you will ruin your immobilizer.