The guts of the pack are pretty much what you’d expect – recovered 18650 lithium-ion cells ... with laser-cut acrylic frames. Rather than spot weld the terminals, [Make It Extreme] used ...

If you are [Danilo Larizza], you strip away the old NiMh cells, and replace them with a custom pack (Italian, Google Translate link) made from 18650 Li ... the more usual spot-welding, sadly ...