As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MAIN BATTERY CHARGER EICAS STATUS MESSAGE OCCURED AFTER T/O JFK - DIVERTED TO BOSTON. REPLACED MAIN BATTERY CHARGER AND INSPECTED BATTERY GRD CABLE FOR CORROSION, NONE FOUND. BATTERY CHARGER OPS CKS. NML PER M/M PERFORMED OVERWEIGHT LNDNG INSP AND OVERWATER 1 CK.