It had already been "Discovered" many years before and in fact galvanic batteries to generate electricity had been being made for some time and may have been made as long ago as 2,000 years before Ben Franklin was around.
Also he wasn't even the first to fly a kite in a thunderstorm. Several other earlier inventors had died trying the same thing. Franklin fame in flying the kite came from the fact that he made practical application of his experiment with Lighting and the Kite to develope the Lighting Rod to conduct lighting safely to a ground. So he discovered nothing except how to channel lighting to prevent damage to structure and fire.
But this is what you get when you oversimplify education.