1. Gravity is universal on the planet, varying only slightly even in outer space.
2. Gravity does not require any other fuel source like fire requires oxygen.
3. Gravity is directly proportional to mass. So the larger the mass larger the potential energy.
4. Use of gravity generates no by-products or waste materials.
5. Gravity has a consistent quality .so need not to refine. And no
6. Li cells of 3v can be charged.