It is my belief that LiIon batteries exibit positive thermal runaway. For a little less capacity LiPo batteries do not exhibit this thermal runaway problem. They probably were not around when the design and specifications were penned for the 787.
Is it possible that the failure is in an individual cell within the LCO product? Just what if, the charging process is montoring the average of all the cells within the makeup adjusting the charge and rate of charge to this set average read. If we have a cell or group of cells that go into premature death, the overheating would be brutal. Basically cooking them to death. What kind of monitoring system is being used?? One perhaps that would allow this condition.
I am not a battery expert but I was wondering about the effects of the vibration and normal shocks due to the flight and takeoff/landings on the battery. I do know that dropping a SLA (sealed lead acid battery) can cause a lot of damage and internal heating if plates short together, so I wonder about the robustness of the plane batteries...
But this battery had nothing to do with passenger entertainment systems.
I just don't think it's likely to be a load profile issue, because excessive load currents are always protected in well known ways. I also find it hard to believe that the charging circuit could be inappropriate for LiIon batteries, because that would have been a really simple problem to find and would have occurred during the multiple thousands of hours of testing.
What did they find to be the problem in those laptop batteries that burned up? Was it not the battery itself that overheated and failed internally, not caused by external faults?
I hadn't heard any inkling of battery problems during the flight test program, though other teething problems were documented. Apparently one battery blew up in a ground-based test fixture back in 2006 though. It's odd (but far from unheard of) that it would get all the way through flight test without issue and then have two incidents so close together after certification.
There was a time in my career where I had to do a lot of testing of products pre-launch. I followed test scripts, but I also spent time just doing strange and random things to try and break the stuff. I always found more problems with the strange and random part of my test program than with the formal part. Invariably, the ways that I broke the products would end up showing up in the field under conditions not anticipated during design.
I could certainly imaging that a plane full of passengers fiddling with the entertainment system added into the other power consumers could create a different power profile than was anticipated and tested for.
The NTSB site linked to in the article has some interesting info - it shows a report that has a photo of a battery cell with a damaged electrode - internal s/c.
The battery chemistry used is Lithium Cobalt Oxide. I would have expected the safter Lithium Iron Phosphate to be used (or other safer-chemistry) instead in this safety critical application.
I tried to see from the photos what (if any) power conversion electronics were in the battery box, but couldn't see any high-power, only low power circuit boards. Power electronics can ignite.
In other words, no new information, as far as I can tell.
My thinking all along has been that it's not a load issue, because presumably the load currents are protected by fusible links, breakers, or other standard measures. So the problem has to be either in the charging circuit, somehow violating LiIon charging protocol (e.g. continuing to trickle-charge when it must not), or some internal short in the battery pack?
The fact that the load device was ruled out as a cause is perhaps the least surprising possibility.
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