As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAKEOFF, PILOT STARTED TO HEAR WHINE IN OVERHEAD SET, FOLLOWED BY POWER LOSS. UPON INSPECTION BATTER WAS FOUND HAVE INTERNAL SHORT CAUSING BATTERY TO GO DEAD. REPLACED BATTERY WITH SERVICEABLE UNIT. OPS CHECKED ELECTRICAL SYSTEM. FOUND OK