R&D Headquarters
Tutorial battery
Three battery sockets in the tutorial take it. Two of them belong to the lesson on handing items over.
What it is for
Puzzle page: Wellness Check
Where the walkthrough uses it
2-1 Onboarding· step 5both players
Past it: one of you presses the button that moves a cabinet into a ledge you can climb. Take the battery and pass it between the two slots of the transfer machine with its two buttons. Turn the grab wheel: one shutter of the half-way doors opens as the other closes.
2-1 Onboarding· step 6both players
At the exit, put the battery in its slot and pull the two chains, one each. The chain on the battery side only works with the battery in.
Where to find it
No item spot is random: the game files place every item in the same spot in every game. Some items exist several times at once, such as the fuses in the Time Maze. From the game files: the area is loaded at these checkpoints. A door on the way can still be locked at some of them.
How to find it
In the long corridor with the green floor and the orange pipes along the top of the wall. It sits on top of the small green crate against the wall.
5 mSeen from above with the ceiling removed. Yellow ring: this spot. Small labels: other spots of the same item close by (select one to go to it). 
The spot seen from nearby (rendered from the game's own level geometry).
Achievements
Corporate Exercise
Pass the Wellness Check
How it unlocks (spoiler)
Finish the Wellness Check tutorial in the R&D Headquarters and walk out through its exit.
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