As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FRA/NKT AIR TURNBACK DUE TO LEVEL I BATTERY CHARGING ALERT ILLUMINATED DURING NORMAL CRUISE FLIGHT. ELECTRIC SCHEMATIC SHOWED 40V. BATTERY APPEARED TO BE CONTINUOUSLY CHARGED WITH NO DRAW. REMOVED & REPLACED BATTERY CHARGER IAW MM PROCEDURES. PERFORMED EMERGENCY POWER SYSTEM TEST, NO FAULT FOUND.