The common curiosity surrounding the nine-volt battery and the tongue test often leads people to question the safety of licking a battery. While this action is sometimes used to check its charge, it is not recommended, even if the electrical risk from this specific battery type is generally low. The practice, however, introduces a chemical hazard and establishes a dangerous precedent for interacting with other, far more harmful battery types.
The Immediate Physical Sensation
The moment a tongue bridges the positive and negative terminals of a nine-volt battery, a distinct and immediate sensory experience occurs. The sensation is often described as a sharp, metallic taste combined with a tingling or zapping feeling. This reaction is particularly intense on the tongue because its surface is covered in highly sensitive nerve endings and is constantly moist. The intensity of this electrical stimulation varies significantly depending on the battery’s voltage and remaining charge. A fully charged nine-volt battery will produce a much stronger tingle than a nearly depleted one, or a standard 1.5-volt AA battery, which generally produces no noticeable sensation.
Electrical Mechanism of the Tingle
Saliva functions as an electrolyte, a substance that conducts electric current through the movement of ions, effectively closing the circuit between the battery’s two terminals. Because the tongue’s skin is thin and wet, it offers significantly less resistance to electrical current than dry skin on other parts of the body. When the tongue completes the circuit, a small electrical current, typically around 1–2 milliamperes (mA) for a nine-volt battery, flows through the tissue. This amount of current is generally too low to cause serious harm from a common household battery, but it is more than enough to stimulate the densely packed nerve endings in the tongue. The current flow can also lead to a minor chemical reaction, called electrolysis, which decomposes the saliva and further contributes to the metallic or acidic taste perception.
Chemical Hazards and Specific Battery Types
While the electrical current from a nine-volt battery is usually benign, the primary health risk from any battery contact involves its chemical contents. Most common household batteries, including alkaline and carbon-zinc types, contain corrosive materials such as potassium hydroxide or manganese dioxide. If a battery is compromised, or leaking, these alkaline electrolytes can cause chemical burns on the delicate oral tissue. The most severe danger is posed by small, disk-shaped batteries, particularly lithium coin or button cells. These small batteries are uniquely hazardous if ingested, especially by children, because they can get lodged in the esophagus. Saliva then acts as the electrolyte, creating an electrical current that rapidly causes a chemical reaction, generating hydroxide ions at the negative pole. This process leads to a severe, caustic burn, which can perforate the esophageal tissue in as little as two hours.
Emergency Response and Safety Measures
Immediate action is necessary if any battery is accidentally swallowed, particularly a coin or button cell. Symptoms of ingestion may not be obvious, but can include coughing, drooling, difficulty swallowing, or refusing to eat. Emergency medical attention must be sought immediately, even if the individual appears fine, as internal damage can progress rapidly and fatally. For contact with leaking battery contents, the affected area, whether the mouth or skin, should be rinsed thoroughly with running water for at least 15 minutes to dilute and remove the corrosive material. To prevent accidental ingestion, all small batteries and products containing button cells should be stored securely out of the sight and reach of children.