What does electricity taste like? Behind this childish, nearly foolish quest, there is some curious mechanisms of chemistry and physics in play.
We know that sour foods contain acid, and the electrolysis happens when a wet and conducting object shortcircuits a battery. So it shouldn't be surprising to know that when the tip of your tongue touches the anode and cathode of a 9V battery, the taste receptors and cation channels on your tongue will generate the taste of sour as a response of influx protons generated from your saliva.
But not all batteries taste the same. Depending on the type of metal used in the poles and the part of your tongue (different sensory nerves are located in different spots), the taste generated by a mild electric current could be drastically different, anything from sweet, bitter, savory to the sensation of burning.
Source: SciShow via Youtube