The generator wouldn't work? Why?

And yes I know it would require more then 1 person to build up the energy needed to charge the batteries. But I know you can charge batteries with exercise. Just depends on how much is needed.

You could have 12 batteries hooked up to your miners on one end and an alternator on the other end. Then the alternator converts the energy from let's say 20 stationary bikes to stored energy in the batteries. So the bikes don't power the miners directly, but are used to store energy in the batteries. Then you just advertise "free gym" haha