[Zak]

I actually have a Bluetooth speaker that takes a removable 18650. It was branded "Polaris V8", but I think it's a white label product that's no longer in production. It still works, and most other ten year old Bluetooth speakers probably don't.

I'm with you on the risk/benefit calculation. E-waste is bad, and the option to bring a spare battery makes a lot of products more useful. A Li-ion cell can be dangerous if mishandled, but less so than a jug of gasoline or larger power tools.

This can be considerably mitigated by sticking a protection circuit on the end of a cell, which makes it no more dangerous than the proprietary Li-ion batteries used in things like cameras.