I'd be interested to know if a headphone battery can suffer thermal runaway. If the surface area to volume ratio is high enough, however badly it is made doesn

I'd be interested to know if a headphone battery can suffer thermal runaway. If the surface area to volume ratio is high enough, however badly it is made doesn't matter - it's not gonna catch fire anyway. If that's the case, there is no safety issue with the headphones - a 0.5mm safety margin either end of a battery which is only 6mm long is insane anyway - and I don't fault the engineers for looking for other ways to get equivalent safety without compromising in capacity.