B-777 PIC DEPARTS STATION WITHOUT NEW DISPATCH RELEASE RELATED TO THE MAINT MEL'ED APU ELECTRICAL SYS AT ATL; GA.

Narrative

AFTER INITIAL PUSHBACK FROM THE GATE IN ATL (WITH AN FAA ACR INSPECTOR IN 1 JUMPSEAT AND A PLT FROM ONE OF OUR REGIONAL CARRIERS IN THE OTHER); WE NOTED A 'STATUS' MESSAGE ON OUR UPPER 'EICAS' DISPLAY. UPON CALLING UP THE STATUS PAGE; THERE WERE 2 MALFUNCTIONS INDICATED -- BOTH REGARDING APU/APU BATTERY. WE PULLED BACK INTO THE GATE; CHKED THE MEL AND CALLED A MECH. THE MEL INDICATED WE COULD CONTINUE; PROVIDED MAINT DISCONNECTED THE APU BATTERY CHARGER; BUT DISPATCHER APPROVAL WAS REQUIRED BY MEL. I ASKED THE CAPT IF HE WANTED ME TO CALL FOR DISPATCH APPROVAL -- HE SAID NO. SEVERAL MINS LATER; HE DIRECTED ME TO SEND THE DISPATCHER AN ACARS (DATA) MESSAGE. I DID SO; BUT WE NEVER RECEIVED A REPLY. AFTER THE MAINT PROCS WERE COMPLETE AND LOGBOOK ITEMS COMPLETED WE PUSHED BACK. I REMINDED THE CAPT THAT WE DID NOT HAVE DISPATCH APPROVAL YET. HE SAID MAINT WOULD ENSURE WE HAD IT. I KNEW THIS TO BE UNTRUE (ALSO RIDICULOUS); SO I REMINDED HIM AGAIN. A FEW MINS LATER WE STILL DIDN'T HAVE THE APPROVAL AND HE SHOOK HIS HEAD -- 'OK.' I GOT BUSY AND DISTRACTED ON TAXI-OUT AND FORGOT TO FOLLOW UP. WE RECEIVED AN ACARS MESSAGE FROM THE DISPATCHER ASKING FOR CLARIFICATION BEFORE TKOF; BUT THE MESSAGE WAS RECEIVED JUST AS WE STARTED THE TKOF ROLL. WE RESPONDED TO THE MESSAGE AND RECEIVED SUBSEQUENT DISPATCHER APPROVAL -- WELL AFTER WE WERE AIRBORNE. I FEEL I DID MY PART UP UNTIL THE TAXI-OUT WHEN I FORGOT TO FOLLOW UP. I FEEL THE CAPT WAS REMISS IN EVEN PUSHING OFF THE GATE WITHOUT A DISPATCH RELEASE. HE GOT BOTH OF US OUT OF OUR REGULAR HABIT PATTERNS IN DOING SO. AFTER THE FLT; I POINTED OUT TO HIM THAT WE TOOK OFF WITHOUT DISPATCH APPROVAL AND HE SAID IT WAS NO BIG DEAL!