Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft
I was awakened from the bunk approximately 3 hours into my rest and called to the flight deck by the Captain. Once we opened the bunk door there was a strong acrid metallic smell in the cabin. Most likely Potassium Hydroxide (Toxic) fumes from the main battery. Once on the flight deck I and the other IRO were apprised of the situation. Fumes and the main battery discharging with a list of associated system failures. The two IRO's started looking for alternate airports. There were not a lot of options. The closest was not a good option; but with Dispatch and Maintenance concurrence we agreed on ZZZZ airport with another airport as a backup in case the weather went south. At this point we told ATC that we were changing our destination to ZZZZ. Landed overweight smoothly. APU would not start. No nose wheel steering. Towed to hard stand. Passenger got off. Crew and FAM's spent 8 hours waiting to deplane. FAMs required [staying] on AC until next day.
Enroute the main aircraft battery started to overheat and discharged. This lead to multiple systems failures. Non normal checklists were completed. An emergency was declared and the flight was diverted to a suitable airport in ZZZZ. Landing was without incident and the aircraft was towed to the ramp.
B777 flight crew reports a main battery overheat and discharge causing multiple system failures and fumes in the cabin and flight deck. Flight diverts to a suitable alternate.