CFI OF SMA TRAINING ACFT LOST RADIO COM DUE TO ACFT ELECTRICAL FAILURE IN NIGHT VFR CONDITIONS.

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I WAS PRACTICING INTXN HOLD OVER L1 SOUND AT THE BELTT INTXN. DUE TO THE HAZY CONDITIONS AT THE TIME; I REQUESTED NY APCH TO KEEP MY ACFT ON RADAR SURVEILLANCE. THEY OBLIGED WITH A TRANSPONDER CODE AND SUBSEQUENT TARGET ADVISORIES. WHEN THE AMMETER WENT TO 0 CHARGE I CALLED NY APCH. THEY DID NOT RESPOND ALTHOUGH I COULD RECEIVE THEM CLRLY. SHUTTING DOWN ALL EXCESSIVE ELECTRIC LOAD I HEADED SW TO FRG. NY APCH WAS NOW CALLING MY ACFT NUMBER AS THEY LOST MY RADAR RETURN. I FLEW DOWN RWY 19 AT 1600 FT AGL FLASHING A FLASH LIGHT AT THE TWR. TURNING TO A R DOWNWIND TO AVOID THE TFC THAT WOULD BE ON THE PREFERRED L DOWNWIND. I COULD FAINTLY HEAR THE TWR CALL OUR ACFT NUMBER RWY 19 AND WIND INFO. I ASSUMED THIS WAS A CLRNC TO LAND ON 19. IT WASN'T; THEY WERE CALLING IN THE BLIND HOPING TO HELP ME. SURPRISINGLY; I COULDN'T RECEIVE ATIS. CHKING DOWNWIND AND BASE I DID NOT SEE ANY OTHER ACFT. ON SHORT FINAL I TURNED ON THE LNDG LIGHT. ALTHOUGH DIM AN ALERT TWR CTLR; SAW MY LIGHT IN TIME TO SEND A SMALL TRANSPORT WHICH HAD BEEN ON L DOWNWIND AROUND. THIS WOULD HAVE BEEN A NOTHING INCIDENT IF I HAD MY HAND-HELD TRANSCEIVER. IT WAS LEFT AT HOME BECAUSE THIS WAS A LCL FLT. THIS WILL NEVER HAPPEN AGAIN.