Most of the gym equipment I use, with the exception of treadmills and stair climbers, is powered by the operator. It only turns on after using it for half a minute.

Phones and tablets need 10 watts or less. A notebook somewhere between 25 to 50 watts if it is running at 100% CPU. Why would an exercise machine with a similar screen size need more than that? Even a total beginner can generate far more than 50 watts.