C172 INSTRUCTOR AND STUDENT HAD INDICATIONS OF ALTERNATOR FAILURE. THE ACFT OP WAS CONTINUED UNTIL THE BATTERY DIED.

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AN INFLT ELECTRICAL FAILURE OCCURRED FOR THE ELECTRICAL CHARGING SYS OF THE C172. THE AIRPLANE JUST HAD AN INSTALLATION OF A GARMIN 430 MOVING MAP; DAUTRON DIGITAL CLOCK; AND GARMIN INDICATOR. ACFT CHKED OUT NORMALLY WHEN PREFLTED AND RUN-UP AMMETER INDICATED NORMALLY WHEN FIELD SWITCH TURNED OFF DURING GND CHKS. BATTERY HAD LESS THAN 10 HRS OF OP ON IT SINCE NEW. NOT MUCH DISCHARGE OCCURRED DURING THE 5-6 CIRCUITS OF FIELD OFF. IN CRUISE FLT; DISCHARGE LIGHT WAS DIMLY LIT. ALTERNATOR FIELD ROCKER SWITCH WAS CYCLED 3 TIMES. SYS SEEMED TO BE BEHAVING NORMALLY; BUT ELECTRICAL EQUIP THAT WAS NON ESSENTIAL WAS TURNED OFF. AFTER 1 HR AND 10 MINS OF FLT; RADIO RECEPTION AND XMISSION CAPABILITY WAS LOST. SQUAWKED 7600 INTERMITTENTLY. WHEN GARMIN GNS LBO WENT OFF LINE; COM RECEPTION WAS RESTORED LONG ENOUGH TO GET VECTORS FROM GREER APCH TO A LOC RWY 1 AT GMV. NAV RECEPTION OF #2 NAV/COM WAS LOST WHILE DSNDING THROUGH CLOUDS. HANDHELD GARMIN III PLT WAS USED FOR EMER COURSE GUIDANCE TO LOC MINIMUMS AT GMV. A NORMAL LNDG AT GMV WAS THEN EXECUTED ONCE VISUAL.