As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE IN THE HANGER AND PERFORMING MAINTENANCE ON A DIFFERENT SYSTEM, NOTICED THE RIGHT BATTERY VOLTAGE DROP FROM 28 VOLTS TO 19 VOLTS RAPIDLY. TURNED THE BATTERY SWITCH OFF AND SHUT OFF POWER TO THE AIRCRAFT. VISUAL EXAMINED BATTERY AND THE BATTERY CASE WAS VERY HOT. DISCONNECTED THE BATTERY AND REMOVED FROM THE AIRCRAFT.