If you've ever gotten into electronics hacking, you've probably had the illusion of most gadgets ruined for you. For example, 9V batteries are basically just six AAAA batteries taped together. As Reddit user usgiorgi points out, many larger store bought batteries contain a collection of smaller batteries. For manufacturing reasons this makes sense. It's also handy if you're building a project and need to tweak your power source.
The rest of the components are also handy. Reddit user CaptainKozmoBagel points out that you can salvage the top of a dead 9V battery to make a new 9V connecter with just a bit of wire. Keep in mind, that you shouldn't tear into just any old battery. Lithium ion batteries (like the kind in your phone) can explode if you try to open them up. 9V batteries, though, are pretty safe to tear down.