Small batteries energize many household and personal items so keep them tested.
Remove the button battery from the device and read the front to determine what the voltage should be; in this example it is 3V.
Set the multimeter to the DVC scale and the range that's higher than 3V.
The bottom of many button batteries is -, and the top and edge are + so you can touch the probes to these locations to get a voltage reading.
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.
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.
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 to 3 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.
To test a button battery:
Look on the battery to determine the battery voltage.
Touch the red multimeter probe to the battery's + side and the black probe to the - side. If the reading is more than 10 percent below the rated output (2.7 volts for a 3V battery), the battery is bad and should be replaced.