Many small gadgets are powered by miniature batteries, often called button batteries because they are as small as a shirt button. They power watches, calculators, toys, palm computers, electronic notebooks, computer clocks, some cell phones, and many other household items. They are everywhere. Lucky for us, they are easy to check and replace.

How Does It Work?

A battery stores and delivers electric current. All batteries contain two electrodes and an electrolyte, which produces the chemical reaction with the electrodes resulting in a current. In "dry" batteries, the electrolyte is a paste of powdered chemicals. A battery's voltage depends on the metals that are used in its electrodes and the number of cells.

Remove the button battery from the device and read the front to determine what the voltage should be; in this example it is 3V.

A button battery contains powdered zinc and mercury oxide with an alkaline electrolyte. The zinc loses electrons as it becomes zinc oxide, while the mercury atoms gain electrons as the mercury oxide changes to mercury. Button batteries typically produce 1.35 volts. One side of the battery is marked with a [+], the positive side, and the other is the negative side. Button batteries are round, but come in various heights and widths.

What Can Go Wrong?

Like other consumer batteries, they either work or they don't. They aren't rechargeable, so fixing one means replacing it. In addition, button batteries can corrode, losing their electrical connection. In extreme cases they can leak, damaging adjacent components.

Caution!

When replacing a button battery in a device, always replace it with the same size and type, indicated by the battery model number, typically etched on the top side.