I took apart an old bluetooth speaker set, took the gumstick receiver/amplifier/battery charger combo, and slapped that into a set of headphones with an 18650 c

I took apart an old bluetooth speaker set, took the gumstick receiver/amplifier/battery charger combo, and slapped that into a set of headphones with an 18650 cell on each side. Lasted days straight. That was a decade ago. I'm surprised nobody's bothered to make large cans with large battery capacity.