What's inside a 9v battery?

Necropsy subject: codename "Bunny". Backup battery for an alarm clock, only putting out 3v. The casing is just a folded over seam. Pry it open and...

Individually shrink-wrapped regular-shaped batteries.

Contacts are riveted to that end piece. It's tough; I can't bend it with my bare hands.

Internal traces are foil on wax paper or something similar wrapped around cardboard. You can also see the crap growing on the ends of the cells. These were doing about 0.5v each and should be at 1.5v.

More traces at the other end going cross-ways to the first set - wired in series. Red is a rubber spacer to force things together, and another of those stiff black ends.

The mini-cells are 7.8mm by 39.8mm, which puts them right around the size of AAAA cells (yes, quadruple A is a size). They're probably a little short for not having the traditionally-shaped end bits and a brand wrapper.