I remember this episode for some reason

a 'stranger' checks into a motel or something.

he has a briefcase.

somehow the inquisitive people at the hotel get ahold of it.

its transluscent, but provides a constant source of electricity.

naturally they have to 'figure out' how it works but the material is unbreakable.

so some wag decides the best source of power to crack the gadget open is....
the brief case. they 'succeed' and in so doing render it nonfunctional. but still dont know how it works; there are no apparent differentiated parts to it, just a transluscent slab.

I dont know why but this episode stuck in my mind all these years.

and now we have astonishing lithium ion batteries that power watches and electronics for years.

I also remember being enthralled as a young boy by the tone of the narrator and eagerly looking forward to that evening's episode.

'the good old days'