Batteries
There have been several previous examples of primary (non rechargeable) lithium batteries catching fire without any obvious provocation on aircraft and elsewhere ( a couple in torches IIRC).
I am not convinced by the statements on grounding and 'short circuits' etc. It is perfectly easy to provide both Thermal and Overcurrent protection to protect the Cells and therefore the system from excessive current being drawn and I am quite sure any decent designer would have done just this. Unfortunately neither protection helps if the cell structure breaks down internally and generates its own fire hazard, at that point containment or ejection are the best bets.