Watch batteries are small round batteries used in electronics such as watches, desktop computer motherboards, PDAs, toys, calculators, remotes, and hearing aids. They come in different types and have varying diameters and heights. Two popular watch batteries are lithium and silver oxide.
Batteries have positive and negative terminals. In watch batteries, the positive side is usually marked with a plus sign and the battery type. The negative side is normally less shiny and smoother than the other.
The voltages of watch batteries are typically 1.5 or 3 volts, and may be checked using a multimeter.
Switch the multimeter on. Make sure that it is on a DC voltage setting, which may be indicated by the letters DC or a short line placed above three side-by-side smaller lines.
Place the instrument on a setting of at least 3 volts. On a multimeter, the side of the dial used to do voltage measurements is usually indicated by a V.
Hold the red probe of the multimeter against the positive terminal or side of the lithium battery. Hold the black probe against the negative terminal. One way to do this is to lay the battery flat against one probe, while placing the other probe on top. Another way is to hold the battery upright using an insulator such as plastic, rubber, cardboard, or wood, and then placing the probes on each side to do the measurement.
Record the voltage. Fresh lithium watch batteries are typically around 3 volts.
Repeat Step 3 but with the silver oxide battery. Fresh silver oxide batteries will be around 1.5 volts.
Turn the multimeter off.
A way to see if a watch battery has a minimum voltage is to test it with an LED. Carefully place both legs over the battery sides, being sure to place the positive side on the plus side of the battery. Some LEDS will not light unless they have a minimum voltage such as 1.7 or 3 volts.