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Early days: < 1600
The Baghdad Battery is an artifact from between 250 BC and 250, discovered near Baghdad, with a structure similar to that of a modern battery. It also appears that similar batteries can be located around ancient Egypt, where objects with traces of precious metal electroplating have been discovered at different locations.
In 1938, the German archaeologist Wilhelm Konig reportedly excavated the five-inch (13-cm)-long clay jar in Khujut Rabu, near Baghdad, Iraq (though some reports say it was found in the collections of the National Museum of Iraq). The jar contained a copper cylinder, in turn covering and protecting an iron rod, isolated from the copper by asphalt. The artifact had been exposed to the weather and had suffered corrosion.
Konig published paper reporting the mechanism's resemblance to a battery in 1940. Upon publication, Konig's discovery was discounted by the scientific community and soon disregarded. Such ancient knowledge in the history of electricity bears no known continuous relationship to the development of modern batteries. Its form, though, is nearly identical to the principles that are in use today. After the Second World War, Willard Gray demonstrated current production by a reconstruction of the inferred battery design when filled with substances, like grape juice. Subsequent tests found acidic residues in the original, analysed as an electrolytic solution, perhaps vinegar or wine.
Some people regard the Baghdad Battery as an anachronism (appearing to be out of place in time), because of the belief that ancient civilizations did not have electrical power and therefore would not have had a device that operated on the principles of electric power. The practical uses of this battery are uncertain. Some contemporary researchers have renewed interest in interpreting this artifact, and suggested electroplating precious metals as a practical use for early batteries by Baghdad Parthians (who used it to electroplate metallic items; e.g. put a thin layer of gold over an object made out of some other metal). Artifacts from ancient Egyptian sites, similarly resembling batteries, or bearing traces consistent with precious-metal electroplating, may support that.
Ark of the Covenant
Speculations that the Ark of the Covenant may have operated as an electrical capacitor are common amongst some electrical engineers (Nikola Tesla being the earliest); they say that the design of it allowed it to store electric charge, and thus could facilitate an electric discharge between the cherubs. The theory suggests that it resembles a capacitor (of radiant energy) in its construction. The biblical accounts of individuals sudden deaths from touching the Ark could correspond to death by a lethal high voltage charge. Louis Ginzberg’s "Legends of the Jews" has ancient oral traditions referring to "sparks" from the cherubim. These "fiery jets" occasionally burned and destroyed close objects. Other biblical accounts could correspond with exposure to some high frequency electromagnetic fields. Jewish legend has occasional records of a "cloud" between the cherubim. The Ark was considered dangerous at these times and Moses would not approach it.
Tesla, in the article "A fairy tale of electricity" (published September 9, 1915), stated in regards to the Ark:
- "The records, though scanty, are of a nature to fill us with conviction that a few initiated, at least, had a deeper knowledge of amber phenomena. To mention one, Moses was undoubtedly a practical and skillful electrician far in advance of his time. The Bible describes precisely, and minutely, arrangements constituting a machine in which electricity was generated by friction of air against silk curtains, and stored in a box constructed like a condenser. It is very plausible to assume that the sons of Aaron were killed by a high-tension discharge, and that the vestal fires of the Romans were electrical." 
Archaeological discoveries of the last century (which include the Baghdad Battery among others), indicate that a working knowledge of energy devices might have been present in ancient Middle Eastern cultures, and therefore it might not have been beyond Moses' specialized training in the house of Pharaoh (Exodus 2:10).
It is known that the acacia wood acts as an insulator, while the gold (the purest available at that time) is known as a good conductor. An electric charge could have accumulated from constant exposure to static electricity in the Middle East climate (among other possible sources). The Ark's upper surface has a rim of gold (a single coil of angels figures). Over the ark, the cherubs could form a spark gap, producing a dynamic radiance that would inspire awe in the observer, and act as a lightning source to kill anyone that touched it.—Num. 7:9; 10:21; 4:5,19, 20; 1 Kings 8:3, 6; Lev. 16:2; Num. 7:89; 2 Sam. 6:6, 7.
Around 1999, author Richard Andrews built a model of the ark. He claims that when tested, it demonstrated that it would act as an electromagnetic accumulator.