The literature on electrical energy storage (EES) is technical and complex, which this paper aims to simplify. It quantifies the current scale, costs and value of different types of mature EES and compares them to peaking generators, interconnectors and demand-side response. Worldwide, dams have 2700 times the storage capacity of pumped storage, which accounts for 99% of conventional EES, batteries making up most of the rest. Indirect use of hydro power, and in future, electric vehicles, adds to their value and if accessible at reasonable cost, would be cheaper than conventional EES. EES, peakers and DC interconnectors can offer flexibility services which considerably enhance their value, but hopes of a battery revolution enabling a smarter electricity system should not be exaggerated.