These are wired parallel, so it’s supplying the same voltage as two batteries, but will only last half as long before dying. It wouldn’t turn on at half voltage in series.
Still gonna have mild power problems though cause the battery isn’t seated well and will possibly short out when you move the mouse.
True… But one of those “energy losses” is producing the sounds itself. So theoretically if you play with them in a vacuum without gravity, they will bounce forever but produce no sound (no air to carry the waves anyway).