Electrochemistry is the science behind batteries and fuel cells. Those devices are needed in green solar energy or wind energy schemes, which are inherently unstable or uncertain power sources. Batteries provide backup through a process known as load leveling. A Ragone chart visually shows the characteristics of electrical storage devices plotted as the logarithm of energy storage density (expressed in Wh/kg) against the logarithm of power producing density (expressed in W/kg). Lead-acid batteries are familiar but are too heavy and store too little energy for their size. The electrochemical series is useful in predetermining the voltage of a battery or the potential required for electroplating an element, such as nickel. Modern batteries are based on lithium or hydrides. Their superiority is clear on a Ragone plot. Fuel cells are reversible and continuously refueled batteries generally consuming (or producing) hydrogen and air (oxygen). A proton exchange membrane (PEM) is their key technology. Key Words: Batteries, fuel cells, green solar energy, wind energy, load leveling, Ragone chart, lead-acid battery, electrochemical series, lithium, hydrides, proton exchange membrane (PEM), anode, cathode, ultracapacitors.