OK, it’s a cheap gimmick, but I’d market these with a simple plug that could connect to an exercise bike, treadmill, or other home exercise device. Yes, I know that you’d have to bust a gut exercising to generate dime’s worth of power, but i’ll bet the idea would sell.
Similar ideas might be a little hydro power generator one could install in water pipes....water flows and store the resultant energy in the batteries. Not much energy but a gooo gimmick.