This was no small fire. It seems to have burned through the hull; the image shows the ribs. No public explanation for the fire has been given yet, but we know from reports that it does not appear to have anything to do with the main batteries. The investigation is being led by the UK’s Air Accident Investigation Branch (AAIB).
The 787 is a complex airplane in electrical terms, as this Boeing chart illustrates. Moreover, it is not commonly known that the 787 uses 30% more power than then much larger A380. The 787 is truly an “all-electric” airplane.
According to the WSJ, there are several electrical parts that are located near the fire location including two remote power-distribution units and three remote data concentrators. In the same article, the vendors for these parts, GE and UTX, were quoted saying that neither had been contacted by the AAIB regarding the fire investigation.
At present it appears, from reports, that an area of focus will be the galley below the burnt area. According to Seatguru.com, the layout of the 
Ethiopian 787 looks like this. As one can see, the back of the cabin, where the burnt area exists, is above the rear galley.
But, at this stage, the galley can be only one area of attention for the AAIB. The investigation process is going to be deliberate and painstaking. The 787 is going to get more attention than any other airplane because of its record. The investigation may show the 787 has more issues with its electrical systems.
Once the cause is identified the repair phase will start. Boeing has a well-established process to fix the 787 from damage, like “ramp rash”. This fire damage is not quite the same. It is unclear at this stage how much damage there is below the skin – the damage may be more extensive than can be seen. The fire could have been burning for a while before the smoke was seen and the fire extinguished. As intriguing as the cause of this fire has been, so will be the repair process.
Thank you for the layout, first I have seen and it gets into perspective. Also if the electrical units mentioned could be shown.
They have to have some idea and people have a right to know ASAP so they can make a decision to fly or not.
What no one has said is why no smoke damage to doors on either side seen including the left side one very close proximity. It would lend to speculation it was an electricl system in the top of fuselage not galley.
Secrecy is plain bad for everyone.
I think a high level discussion with a ton of lawyers sitting by is going on about the communication. Just like after the JAL battery. The stakes are enormous.
Apparently a lithium battery in a Honeywell beacon went up. But it was not lithium ion.
Looks like those need to be replaced. If the beacon can be inop while they cert a replacement battery, the fleet will be fine. If the beacon cannot be inop, then the FAA has a major quandary.
Who alleged that it was the ELT battery? Honeywell has been in this business for many years and the product is quite mature. The lithium battery used in an ELT is an ultra-low self-discharge device with a 12-year self life. It’s been used in thousands of exemplar ELTs since about 2005.
I would be skeptical of any assertions about the ELT unless made by somebody who personally saw the ELT carcass that exhibits evidence of an internal energy release.
What we appear to have is anohter Li Ion battery thats gone bad.
I would think all of them would be pulled until it can be confirmed as there is in my mind a huge question as to if they are needed at all (does anyone loose track of a large jet these days? Its on a fixed flight path).
It does bring to question the use of those type batteries unless protective systems in place (and only justified by main power batts per the recent mod).
How many other Li ion types are on not only the 787 but any other plane and should they even be used?
Airbus gave them up on the A350 (though test planes do have them) but there are two large ones on the A380 that no one is talking about.