Interesting reports... But these batteries seem to have exploded without fire, probably they just build up pressure until the housing popped.
Hydrogen is usually not a big danger - yes it easily ignites but it also diffuses away from its source in no time. And if a small volume of hydrogen burns then it´s just a very short flash, very hard to imagine that this lights up a book. Lead acid batteries generate quite a large amount of hydrogen/oxygen mixture, and its danger is much more spraying around the sulphuric acid than setting anything on fire.
I think its not common but also not impossible that an overloaded 0402 resistor wrapped in paper sets something on fire. Heated paper really is a good fire starter.
Thanks, that is a very thoughtful and good post!
Unfortunately, I think we are (or at least me), like back seat drivers, or it is all too easy to comment, when sitting at ones couch.
If any entity gets serious about investigating this fire incident. They would need to process all the available evidence and information.
As regards the batteries, being involved.
There are lots of possible ways (many already mentioned in this thread). Such as electrical over-heating, setting fire to something, a Hydrogen explosion (as you said, the vast bulk of the time, it does not set anything on fire, but there is a small or tiny risk, that maybe it could or did), even theories that the same Chinese battery factory, handles (makes) Lithium batteries as well, and such material ended up in the fire starting battery cells.
There are also many other causes of car fires, including its electrical wiring, fuel leaks catching fire, a fire underneath the car for some reason (almost certainly would have been noticed and caused different fire effects), the owners setting the car on fire for reasons (such as insurance fraud), etc.
Hopefully and if necessary. The investigators can get any research professionally done by experts, as necessary, if they deem it necessary.
As regards this thread, my gut feeling (I could easily be wrong), LR44 batteries are too weak and low capacity, electrically speaking, to readily (ignoring a super-rare accident), heat stuff up (or itself), enough to pose a serious fire risk.
On the other hand, (as already mentioned), 700 milliamps, is more than I was expecting, from such a tiny cell, especially with it being Alkaline. Even much bigger Alkaline cells, don't seem to have anything like as high short-circuit currents (IIRC, I managed to get around 5 .. 10 Amps, from a fresh Alkaline C cell, of decent brand), compared to most rechargeable battery types, such as Lead-acid batteries, which give out crazy amounts of current, if necessary.
EDIT: Much editing, lots of typos and made shorter.