C172 PLT COMPLIED WITH ALL PROCS FOR DEPARTING AN ARPT WITHIN DC ADIZ. AFTER TKOF HE FOUND THE ACFT HAD HAD COMPLETE ELECTRICAL FAILURE; THAT RENDERED HIS RADIOS AND XPONDER INOPERATIVE.

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ON 03/SAT/03; AT APPROX XA45 I CONTACTED BWI CLRNC DELIVERY TO OBTAIN A XPONDER CODE AND ATC FREQUENCY TO DEPART FROM THE MONTGOMERY COUNTY AIRPARK GAI AIRPARK INSIDE THE DC ADIZ FOR A FLT HGR. THE PURPOSE OF THE FLT WAS TO DELIVER THE ACFT FOR ITS ANNUAL INSPECTION. I RECEIVED CODE AND FREQUENCY 128.7; WAS TOLD TO HEAD TOWARD FDK UNTIL OUTSIDE THE ADIZ AND I DEPARTED GAI. UPON TURNING CROSSWIND AT ABOUT 1000 FT MSL; I ATTEMPTED A CALL TO ATC AND RECEIVED NO RESPONSE. I FIGURED I WOULD HAVE TO GET HIGHER BEFORE THEY COULD HEAR ME. I CONTINUED MY CLB ON COURSE TOWARD FDK AND CONTINUED TRYING TO REACH ATC ON 128.7 TO NO AVAIL. I THEN NOTICED THAT READOUTS ON BOTH RADIOS WERE ALTERNATING BETWEEN DIM AND BRIGHT. SINCE THIS ACFT HAS A 12 VOLT ELECTRICAL SYSTEM; BUT HAS 28 VOLT RADIOS POWERED BY A SEPARATE POWER SUPPLY; I BEGAN TO THINK THE PWR SUPPLY HAD GONE BELLY-UP. I ATTEMPTED SEVERAL TIMES TO CONTACT ATC VIA A HAND HELD RADIO; BUT WAS UNABLE TO DO SO; PROBABLY DUE TO HAND HELD'S RELATIVELY LOW PWR. AT THIS TIME; I REALIZED I HAD SUFFERED A COMPLETE ELECTRICAL FAILURE AFTER NOTICING THAT BOTH FUEL GAUGES WERE PEGGED ON EMPTY AND NOTHING THAT WAS ELECTRICALLY PWRED WORKED. SINCE I WAS NOW OUTSIDE THE ADIZ; I RESUMED MY PLANNED COURSE WHICH WAS GAI - BURGY INTXN HGR. I SELECTED THIS COURSE TO REMAIN OUTSIDE THE ENLARGED P40 AIRSPACE. I WAS EXPECTING TO BE INTERCEPTED AT ANY MOMENT; BUT NEVER SAW ANY OTHER ACFT DURING THE FLT. UPON REACHING THE AREA NEAR HGR; I WAS FINALLY ABLE TO REACH THE HGR TWR VIA MY HAND HELD WHEN I WAS ABOUT 5 MILES OUT. I EXPLAINED MY SIT AND WAS CLRED TO LAND IMMEDIATELY. AFTER PARKING AT THE MAINT FACILITY THAT WOULD BE PERFORMING THE ANNUAL; I CALLED THE HGR TWR AND EXPLAINED WHAT HAD OCCURRED IN DETAIL. THEY TOLD ME THEY HAD NOT HEARD FROM ANYONE ATTEMPTING TO FOLLOW-UP OR CHK ON ME. I DON'T BELIEVE THERE WAS ANYTHING ELSE I COULD HAVE DONE IN THIS SIT. THE ACFT HAD BEEN FLOWN A WEEK PRIOR WITH NO PROB AND THERE WAS NO INDICATION OF ANY PROB UNTIL IT OCCURRED.