The earliest known application of chemical energy to produce electricity, dating back to a period between 250 BCE and 640 CE, was known as the Baghdad Battery. Modern day batteries are improvised versions of their ancestors, devised by the Italian physicist Alessandro Volta, during the 1800s. Volta initially termed the invention as the Voltaic pile. A battery stores chemical compounds that react with each other to produce an electrical current. A typical battery comprises of electrochemical materials, such as one or more galvanic cells, fuel cells, or flow cells. Manufactured according to different needs and implementations, a battery is available in size such as the A-series (A, AA, AAA, AAAA), B, C, D, F, G, J, and N, 3R12, 4R25, and rarer varieties, such as PP3 and PP9, and the lantern 996 and PC926. The AA battery is commonly used in most portable electronic devices. Pronounced as 'ay-ay' or 'double A', it is a dry-cell with a discharge of 1.5 volts providing a 1800 to 2600 mA'¢h charge delivering capacity. The rechargeable variant of this size generates 1.25 volts with a delivery capacity between a range of 650 to 2700 mA'¢h. An AA battery is 1.97 inches in length and 0.56 inches in diameter weighing almost 0.81 ounces. Widely used and preferred by people are the rechargeable types of batteries, due to the repeated utility offered by them. A rechargeable battery varies in capacity depending on the chemical compounds used. The most common Nickel-cadmium (NiCad) AA batteries provide 650 to 800 mA'¢h and last for a shorter period. The rare and more expensive 800 to 1000 mA'¢h NiCad batteries last much longer. Another variety is the Nickel Metal Hydride (NiMH) battery that delivers 1400 to 2700 mA'¢h, providing longer usage times as well as shorter recharge cycles. Though NiMH lasts longer, the older NiCad variety is more suited to device with high current requirements. Recent developments in technology have seen the introduction of the Lithium-Ion (Li-ion) batteries. Pioneered in 1912 and mass produced since 1991, first by Sony, Lithium-Ion batteries are lighter and provide the best energy-to-weight ratios for delivering electric energy.