As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED COMPLETE COMM FAILURE AS WELL AS TRANSPONDER REPORTED INOP BY ATC. PILOT RETURNED TO FRG WITHOUT INCIDENT. INSPECTED AND FOUND BATTERY VOLTAGE BELOW 10 VOLTS. STARTED AIRCRAFT WITH GPU. ALTERNATOR LIGHT WAS ILLUMINATED. ALTERNATOR WAS REMOVED AND REPLACED. AIRCRAFT BATTERY WAS REMOVED AND SERVICED. AIRCRAFT WAS GROUND RUN. OPS CHECKED OK.