3x Battery Teardown article shows you what is inside different batteries. So if you open up a 9 V battery, you find 6 thin 1.5 V cells inside.
But what was inside that lantern battery, the rechargeable PP3, or the funny shaped lump on the back of my laptop? Check 3x Battery Teardown article to see.
If you plan to do your own opening, there video of how to open your laptop battery case and other article how to repair laptop battery. Before trying to do anything with laptop batteries, read also about Safety Concerns and Protection Circuits.