This is your simulated circuit, not your real circuit. The real circuit would have a battery (what voltage/size?) and I'd like to see how it is connected, e.g. is the -ve terminal of the battery connected to 0V? Also, what kind of crystal did you use, was it the small cylindrical ones, or HC49/U style? What supply does the DS1307 run from when it is powered from the main supply? None of this information is available from the circuit diagram. Also, can you post a photo of the DS1307 portion of your hardware?