Arduino due DS1307 RTC library

We're talking on 2 different things.

I didn't know that the SAM3X has an RTC built in it.
I've tried to connect a DS1307 to the Arduino Due.
That is why I didn't understand how your library can help me with my project.

If there is a RTC built-in, how can I save the time there. is there a way to connect a battery to the SAM3X, like the one connected to a DS1307 circuit?

Thanks.