This document provides an introduction and over view of state-of-the-art energy storage technologyincluding a comparison of them and various evaluations of the new possibilities they give to the energyinfrastructure and to society. It also describes which function each energy storage system is best suitedfor and which needs they can fulfill in our modern world. As a follow up, basic concepts about batteriesare explained and a methodology to evaluate the capacity of most types of rechargeable batteries isdescribed along with the design of a device required.