BE55 INSTRUCTOR REPORTS TOTAL ELECTRICAL FAILURE WHILE PRACTICING NIGHT LANDINGS WITH STUDENT. STUDENT LANDS UNEVENTFULLY WITH NO LIGHTS.

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WE WERE MAKING A NIGHT XCOUNTRY. THE XCOUNTRY WAS TO INCLUDE 5 LNDGS TO A FULL STOP AT A CTL TOWERED ARPT. THE FLT STARTED WITHOUT A HITCH. ALL OF THE ALTERNATORS WERE SHOWING A GOOD CHARGE DURING RUN-UP AND TKOF. PRIOR TO THE PRACTICE ILS APCH; WE CHKED THE INSTS AGAIN. ONE ALTERNATOR WAS SHOWING A REALLY LOW CHARGE; HOWEVER; THAT IS NORMAL FOR THE AIRPLANE. SHUTTING DOWN THE OTHER ALTERNATOR MAKES IT SHOW A FULL CHARGE. THE ILS AND THE LATER PATTERN WENT WELL. WE PRACTICED A LNDG WITHOUT THE PANEL LIGHTS ON THE THIRD APCH TO LNDG. WE PRACTICED A LNDG WITH JUST THE NAV AND BEACON LIGHTS ON THE 4TH LNDG. FEELING GOOD ABOUT OURSELVES; THE 5TH AND FINAL LNDG WAS TO BE A NORMAL LNDG. ON DOWNWIND; WE WERE CLRED FOR THE OPTION EARLY. AFTER GEAR DOWN ABEAM THE TOUCHDOWN ZONE; I REQUESTED A VERIFICATION ON THE STOP-AND-GO CLRNC. AFTER 2 UNANSWERED CALLS; I REALIZED THAT THE RADIO WAS NOT DISPLAYING THE 'TX' ICON. HOPING IT WAS JUST MY PUSH-TO-TALK SWITCH; MY STUDENT MADE 2 UNANSWERED CALLS. WE QUICKLY TUNED THE STANDBY RADIO AND STILL NO RESPONSE. DURING A QUICK CHK OF THE SYSTEMS; WE FOUND BOTH AMMETERS AT ZERO. WE RECYCLED THE ALTERNATORS AND STILL NO RESPONSE. A CHK OF THE LNDG LIGHTS ON THE WING VERIFIED THAT WE WERE ON BATTERY PWR AND FADING FAST. THE LNDG GEAR HAD USED UP ALL THE AVAILABLE WATTS OF PWR. WE WENT DARK ON SHORT FINAL AND WE LANDED WITHOUT THE USE OF OUR ELECTRICALLY OPERATED FLAPS. THE STUDENT MADE AN UNBELIEVABLY SOFT LNDG AND WE EXITED ON THE SECOND TXWY. WE STOPPED SHORT OF THE FIRST INTXN AND CALLED ARPT OPS ON A CELL PHONE AND ASKED FOR ASSISTANCE. WE WERE MET BY THE EMER RESPONSE AND ARPT PERSONNEL FOR AN ESCORT TO A MAINT FACILITY. THE PROB THAT GOT US IS THAT WE DIDN'T CATCH THE ELECTRICAL FAILURE SOON ENOUGH. THE BARON AMMETERS USUALLY READ LOW. THIS IS BECAUSE ALL BUT ONE FLT ARE FLOWN DURING THE DAY AND THE ELECTRICAL LOAD IS VERY LOW. ALSO; ONE ALTERNATOR SEEMS TO READ ZERO AND THE OTHER CARRIES THE SMALL LOAD MOST OF THE TIME. THE IDLE ALTERNATOR SWITCHES EVERY FLT; SO EITHER THE L OR THE R WILL READ ALMOST ZERO IN MOST CASES. EVEN THOUGH IT WAS NIGHT; A LOW AMMETER READING OR ZERO READING REALLY DIDN'T DRAW MUCH ATTN TO ITSELF. I WILL CERTAINLY VERIFY THAT IT IS BECAUSE OF THE LOAD THAT IT READS SO LOW. IT WAS VERY FORTUNATE THAT WE WERE CLRED TO LAND ALREADY AND HAD THE GEAR DOWN. WE WOULDN'T HAVE HAD THE CHANCE FOR LIGHT SIGNALS; BECAUSE DURING A PHONE CALL WITH TWR AFTER THE EVENT; WE WERE TOLD THAT WE WERE INVISIBLE WITHOUT OUR LIGHTS. THE 2 PRACTICE APCHS WERE A GREAT LIFE SAVER BECAUSE THE STUDENT WAS WELL PREPARED FOR THE REAL THING. THE CAUSE OF THE DUAL ALTERNATOR FAILURE WAS THAT THE BELTS HAD COME OFF BOTH ALTERNATORS. THE MECHS ARE LOOKING TO MAKE SURE THAT THEY DON'T FALL OFF AGAIN. I AM NOT SURE WHAT THE CAUSE WOULD HAVE BEEN AND WHAT ACTIONS THEY TAKE TO PREVENT IT. ONE OTHER THING THAT WE SHOULD DO IS HAVE ATC'S PHONE NUMBERS IN THE ACFT WITH US. WE HAD A CURRENT AFD BUT THE NUMBER LISTED WAS THE ARPT OPS AND NOT THE CTL TWR. WITH THE MILLIONS OF CELL PHONES TODAY; THE ABILITY TO CALL THE TWR TO RPT AN EMER WOULD BE A BLESSING. THEN THEY WOULD BE AWARE OF OUR ISSUE AND BE ABLE TO ASSIST US OVER THE PHONE.