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.

How Can I Identify the Problem?

If the device stops doing what it is supposed to do or is no longer accurate, inspect the battery for corrosion or leakage. A discolored, corroded, or leaking battery should be discarded. You also can test the battery to see if it has lost its power (see below) and replace it if it is faulty. To test a button battery, make sure you use the lowest DCV (direct current volts) scale on the multimeter because voltage is very low.

What Parts, Materials, and Tools Do I Need?

Set the multimeter to the DVC scale and the range that's higher than 3V.

The only part you'll need to fix a button battery is another button battery. Tools, however, depend on what the battery is installed in, because you have to gain access to it to visually and electrically check it. Typical disassembly and testing tools for smaller electrical devices are these:

• Screwdrivers
• Pliers
• Wrenches
• Emery cloth for cleaning
• Multimeter

What Are the Steps to Fixing It?

 

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.

Test a button battery:

1. Look on the battery to determine the battery voltage.
2. Set the multimeter to the DCV scale.
3. 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.

 

Fix-It Tip

Check your other button battery-powered devices to determine if they use the same model, and purchase batteries in multiple packs to save money.