tronja307020: I sprung for the artfunk one! Super expensive, but I got a strictly-for-fun cash gift, and given we'd already thrown hundreds into buying electrical tape/components (and hundreds of hours into manipulating it/using it)...
ALSO FriendlyMiGo, having left the thing on overnight, I can confirm that the battery pack lasts awhile! It's still going now, ~14 hours after we turned it on, though I'm pretty sure the lights are getting v. dim.
(Not 100% sure, because it's been dimming gradually over 14 hours and my brain isn't sure if it was ever brighter than this, but I think it was? It's still visible, which bodes well for being able to helmet at the con all day/night on a single battery pack as needed, especially if we don't turn the lights on much in the brighter places/hours.)
(still going now, no overheat, but dim enough that I'm gonna call the test. ~18 hours, by the end of which the glow was visible if standing next to it, but not otherwise.)