MD-11
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 46; Flight Crew Total 9000; Flight Crew Type 3000
Situational Awareness; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Landed As Precaution; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport
Aircraft
I was the relief pilot. Approximately 1 hour and 30 minutes into the flight a level 1 'EMER PWR ON' alert displayed on the EAD. The First Officer and I referenced the QRH for the alert. The QRH says Consequences: NONE and states that the emergency power has been automatically or manually turned on. The emergency power switch was still in the arm position so we knew that the system had been automatically turned on. After the QRH was referenced; I went to the back and got the Captain; as he was on break. The FO and I informed him of the problem. When we first displayed the electrical system; components were operating normally and the battery was showing 29 volts and -39 amps. Approximately 10 minutes later the battery displayed 26 volts and -49 amps. We talked with the company; maintenance; and the MD11 subject matter expert and as a crew we decided to monitor the problem. After about another 20 minutes the battery voltage started rapidly dropping and reached 21 volts with an amperage draw of -60. We contacted ATC via CPDLC; SATCOM and eventually HF and [advised them] and initiated a return. We also coordinated with the company on the return. Shortly after starting the return; we were concerned about completely losing the aircraft battery and possibly having a fire due to a thermal runaway. Due to this; we turned the emergency power switch to off. I would like for there to be more information and guidance in the AOM referring to a battery discharge when the emergency power is on and all other electrical system components are displayed as operating normally.
[Report Narrative Contained No Additional Information.]
An MD-11 crew returned to the departure airport after experiencing an 'EMER PWR ON' event with an associated battery discharge.