I have an early digital video camera with a genius design. It came with a custom rechargeable cell in the battery compartment. But the compartment _also_ supports regular AA batteries.

Most petzl headlamps are setup this way for a small lipo pack or 3 aaa's. It's great

Brother label printers used to support this up until a couple of years ago at least but sadly the most recent models have stopped having the AA compatibility.

Absolutely the best of both worlds. You can find a shop selling AA everywhere in a pinch and keeping a few in the camera bag is easy too.

I‘ve done this with my HHKB. Great solution.

Point taken. What's your review of those batteries with a USB C port? I've always avoided them because of the reduced capacity, price (5 or so years ago) and that I assumed they would have a constant voltage output making it impossible for devices to give you an accurate battery level measurement.

I'm not magic; can't replace built-in batteries without a soldering iron (or at least, relatively uncommon replacement parts).

As always, engineering tradeoffs are involved. I was recently looking for a casual point-and-shoot camera from the ~2010s, but all the slimline ones used flat lithium removable batteries (as only the bulkier ones have space for AAs).