How to open a Dell KJ321 battery pack.

[Hank]

As it says on the tin, I'm absolutely clueless about how to open it, so maybe someone has some bright ideas, or might even have opened one him/herself.

[strawberry]

not made to be opened. break it apart in the way it will be possible to assemble/glue it back together (when repair is planned)
harder to find exact replacement size when it is not 18650 cell

[tunk]

I've taken apart a handful of laptop batteries to salvage the cells.
Usually I start around the battery contact with a screwdriver, taking
care not to short anything, damaging the cells or yourself.
There's some videos on youtube, you could try these keywords:
salvage 18650 from laptop

[mikerj]

The cases are typically clipped AND glued or ultrasonicaly welded together, considerable force is often needed and damage to the casing is likely.  OTOH I have had a few packs that came apart relatively easily with a spudger, but they are the exception.