Next, let's zoom in on that battery board. The two pins on the output connector show 3V, which suggests these are probably CMOS batteries wired in parallel. But why two of them? And why the strange placement in the middle of the enclosure?

Ordinarily, we'd expect to find a single CR2032 battery protecting the NVRAM, like on previous iMacs.

Best guess: The new iMac design was too thin for a CR2032 on the main board. That's right—they couldn't squeeze in the battery from an AirTag. So Apple instead used two half-height CR2016s, and squirreled them away over here for clearance.

Closer inspection reveals a camouflaged stretch-release adhesive pull tab under the battery board—the same sort of stuff that secures iPhone batteries.

We're fans of this stretchy adhesive when the alternative is poking and prying at a glued-down smartphone battery, but its use here seems ... odd.

Once again, thinness suggests an answer: This is a wafer-thin board, set in place with a vanishingly thin strip of adhesive.

You can't fully remove or replace either battery while the board is glued in place. Fortunately replacements shouldn't be frequent, but they'll certainly be inconvenient.