Essentially, you have to heat and break the adhesives holding everything together, then push the atty guts out the bottom of the cylinder (where the cart goes).
To heat it, I use a (clean!) soldering iron. I keep it pressed on the battery connector and/or the cylinder wall for a while. I haven't tried boiling it yet, but probably will the next time.
To push it out, I hammer on a brass rod held against the battery connector. The diameter of the brass rod is the same as the battery connector. You could also use a brass screw, so long as the head is flat and large enough.
The heat usually doesn't break all the adhesive right away, so it's 'heat, tap, repeat' until it breaks free completely. Then it slides out the cylinder easily.