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.
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.