Maintenance Powerplant; Maintenance Airframe
Maintenance Inspector 15; Maintenance Lead Technician 20; Maintenance Repairman 30; Maintenance Technician 30
Troubleshooting; Situational Awareness; Communication Breakdown
Aircraft Equipment Problem Critical; Deviation - Altitude Overshoot; Deviation - Altitude Undershoot
General Maintenance Action
Human Factors; Aircraft; Manuals
[B777 aircraft Main] Battery had severe overheating.
Reporter stated they are Repair Station. The B777 Main Aircraft Battery that raised their concerns had been received in December 2012.  The Fiber Nickel Cadmium (FNC) battery had signs of severe overheating; was scorched and blackened. The external green battery container; which is made of steel and approximately one and one-half foot by one and one-half foot (1' 1/2' x 1' 1/2') in size; had similar discolorations. The interior liner of the container is made of a plastic-type material similar to 'Gill Flooring' material and separates the battery from the steel container. The liner had melted across the top of the battery posts and sidewalls of the green box (battery container); even though the liner material is approximately .060' thousandths of an inch thick.Reporter stated there is only one Manufacturer (MFG) of the FNC type battery used on B777 aircraft. FNC batteries are sealed; 'No-Vent valve battery and are not a Gel type battery. Out of all the FNC batteries they repair; an average of seven FNC batteries a year are found with similar conditions. Batteries with three or more damaged cells; out of twenty-four cells per battery; are not repairable per the MFG. The damaged battery he reported on was not repairable. One of their Electrical Engineer's noted the battery damage was indicative of overcharging and believes the cutoff protection system for the FNC battery's electrical charging cycle is failing. If a FNC Battery has a cell that shorts and continuously demands a charge and starts to overheat; thermal expansion will migrate to the other cells in the battery and the battery will overheat. He does not know if the B777 aircraft's Main Battery Charger System can detect a failed cell or several cells that may demand continuous charge and cause overheating and possible fire in the aircraft's Main Equipment Center (MEC). Reporter stated all the FNC batteries they receive in their Shop come inside the green colored steel battery containers. The batteries had been removed by different Air Carrier Operators of B777 aircraft for either a 'Time Change' requirement; or an 'On Condition' situation due to a battery write-up. But not all Air Carriers were aware of the extensive damage some of their FNC batteries had incurred when their Main batteries were removed for 'Time'; not until they arrived in his Repair Shop. With the recent events involving the B787 aircraft and Lithium batteries; he feels the B777 Main Battery overheating issue has not been resolved and is a safety of flight concern.
A Repair Shop Maintenance Inspector reports about a Fiber Nickel Cadmium (FNC) battery received in their Shop with evidence of severe overheating; scorching and blackened.  FNC type batteries are used as the Main Battery on B777 aircraft.