A C172 ON APCH AT 2500 FT RETURNED TO DEP ARPT DUE TO LOW VOLTAGE WARNING LIGHT ILLUMINATED. 10 NM FROM ARPT RADIOS FAILED COMPLETELY.

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FLYING ALONG AT 2500 FT INBOUND TO ZZZ1. FOR TOUCH AND GO NOTICED LOW VOLT LIGHT CAME ON. ABANDONED APCH. CHANGED COURSE TO ZZZ (ACFT'S HOME BASE). AT ABOUT 10-12 NM NE OF ZZZ RADIOS FAILED COMPLETELY; AFTER GETTING CLRNC FROM TWR SAYING 'PROCEED DIRECT RWY 19.' KEPT ON CURRENT COURSE AND WHEN ENTERING TFC PATTERN AT ZZZ TURNED AVIONICS ON AND THE RADIO WORKED JUST LONG ENOUGH TO HEAR TWR SAY 'CLRED TO LAND RWY 21.' AFTER VERIFYING OUR CLRNC; I LANDED THE ACFT WITH NO INCIDENCE. AFTER TAXIING CLR OF RWY 21; ALL ELECTRICAL EQUIP WAS DEAD; SO I CALLED TWR FROM CELL PHONE TO GET TAXI CLRNC TO THE RAMP. THEY APPROVED. I TAXIED; SHUT ACFT DOWN AND SECURED IT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ON THE APCH THE LOW VOLTAGE LIGHT ILLUMINATED AND WHEN XMITTING; THE LIGHTING DIMMED. ON RETURNING TO THE DEP ARPT THE RADIOS FAILED COMPLETELY. MAINT FOUND ALTERNATOR WAS NOT RESET AFTER EMER PWR CHK ON PREFLT COCKPIT CHK. NO EMER WAS DECLARED DUE TO PAPERWORK CONCERN. THE RPTR STATED HE HAS NOW COMPLETED 2 HRS OF FLT SCHOOL ON C172 ELECTRICAL SYS AND PREFLT CHKS.