Building replacement proprietary battery packs
After getting into drone racing (where you need to take good manual care of your batteries because they're basically a bunch of cells soldered together), I realized that every battery we have everywhere is just some standard cells in some standard configuration.With that knowledge, you can replace the battery in any gadget (small ones are usually 3.7V, or 1S), if you know how to care for it. Replacing the battery in a MiniDisk like this, I would maybe not trust the internal MiniDisk charger and charge by hand, but it should otherwise work identically to the factory battery.