Back-of-a-fag-packet calculation:
Cell voltage 3.7V, capacity 65Ah, mass 2.75Kg, specific heat capacity 1,000J/KgK (guess)
(3.7 * 65 * 3600) / (1000 * 2.75) = 314K
The energy stored is enough to raise the internal temperature 300+degs in self-discharge before you take all the subsidiary exothermic reactions that go with thermal runaway. Looking at videos of disrupted lithium cells it is enough in some cases to take them to white heat and melt metal casings.
I can't see an obvious way to stop the heat bleeding through to other cells - the electrical bonding between them would carry significant flux even if the insulation of the walls was perfect.
As it stands at the moment, my personal opinion is that it is possible to have a safe installation of li-ion batteries in an airliner but Boeing have chosen the wrong chemistry together with inadequate safeguards. I agree with the NTSB that fire on board is something that just isn't acceptable, even if you think it could be contained.
