Fun* fact in this video: the 'disposable' vapes thrown away in Britain alone contain enough lithium batteries to make 1.2 Million e-bikes.
I've been independently powering things with vape batteries that I've rescued before seeing this video. Pull out the cell, add a cheap usb charging module and you have a fully rechargeable 3.7v power source. If you need higher voltage you can put them in series and you can even get multi-cell balancing modules for next to nothing if you want to have a few in parallel for more current.
I don't trust them for anything critical, but they're great for low-budget projects as the cells are completely free. My bike lights are all powered by them (one can run a flashing bike light for a couple of weeks' use), as well as various other things that had their batteries die, or that didn't come with rechargeable batteries.
I also only charge them somewhere flameproof, though I haven't had any issues so far.