Negligible risk Dave. The problem with the original batteries was that they used the best usable cathode material at the time, cobalt. When carefully manufactured that was fine and very efficient, e-bikes used that too. Unfortunately with time and larger scale mass production, standards slipped and minor errors n production could result in a chemical problem arising.
Lithium is potentialy dangerous stuff and it never normally exists in a battery in metallic form, but those manufacturing defects resulted in crystals of metallic lithium forming and growing in the electrolyte. These crystals grow in a jagged way with very sharp projections, so as they grew they could puncture the internal insulation between layers and create short circuits.
With the large capacity in laptop and e-bike batteries those short circuit currents were large, leading to fire, internal breakdown multiplying the shorts and even leading to explosion. This could happen randomly at any time, not just when charging and even when idle in transit, hence the air travel bans and limitations.
The cobalt was hurriedly replaced by manganese which was much safer but less efficient, this leading to the well known period of lithium battery premature failures. Over time they have been improved and compound cathodes have now been developed which can safely include cobalt again. Today's polymer batteries are all of this type and probably as safe as any battery technology.
That said, all high capacity batteries should be treated with respect of course, all types are potentially household bombs if abused.
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