Can I replace the battery in StarGlow?
The battery in the lightsaber is in-built and can’t be replaced. Its capacity is enough to use the device for a long time (10+ fuel charges).
Obviously this is ridiculous.
I mean, I guess it's possible, if the "electronics" are just a simple lighter-style spark gap and an illuminated AV switch. Their channel has a second video where they demonstrate refuelling the saber, which looks like there've got some kind of inbuilt pumping mechanism to draw the liquid fuel from a bottle. so, at a guess, the sum total of electronics are a pump, an ignition system, an illuminated AV, maybe a few safety sensors and a basic microcontroller to keep things working.
I very much doubt they're putting a proper soundboard in there, all the swing sounds on the videos sound dubbed on in post. The "saber" is using only liquid fuel, which I doubt it can hold that much of in a hilt that small. Just a complete wild guess, of course, but I doubt one fuel charge would last more than five minutes. at that point, 10 charges/battery seems kinda viable, for an decent 18650.
But yeah, this sounds like a really stupid idea. Although, if in a few years' time, there's one going cheap on eBay, I'd buy it to gut it and convert it into a proper LED saber. Or convert it into Luke's Jedi Tree burning torch from TLJ.