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You are correct, it eats battery; it lasts about 8 hours or so on li-ion. If you look down the lens and move it around, you can really see the mechanical movement in action.

It has two operating modes.

1, it stays on as long as the button is depressed. This is good for quick looks.

2, you press it once and it stays on until either (a) 5 minutes pass, or (b) you press it again, or (c) you put the binoculars down (it knows when they are vertical, like hanging around your neck.)

Image stabilization does indeed eat batteries.

I understood it needs to remain pressed.

Not true. Press briefly and it stays in IS mode for a couple minutes.