How to Test a Laptop Battery

by Josh Fredman

    Batteries are one of the weak links in laptop computers. When you’re away from an outlet, your ability to use your computer is completely limited by the amount of battery power available. Batteries also tend to wear out faster than other laptop components, typically exhibiting performance degeneration with just two or three years of use. Once the performance gets bad enough, you’ll need to replace the battery. It’s fairly easy to test your battery’s charge and health, and by doing so you can help avoid unwanted surprises.

    Checking Battery Charge in Windows

    Step 1

    Click on the Windows button to open the Start Menu.

    Step 2

    Look for a search bar that says “Search programs and files” at the bottom of the Start Menu.

    Step 3

    Type “Windows Mobility Center” into the search field. When the results come up, click on “Windows Mobility Center” in the Programs section at the top of the results. Windows Mobility Center has various indicators to show whether your laptop is mobile.

    Step 4

    Look for the “Battery Status” indicator. This shows you what percentage of battery power you have remaining. If you typically keep your laptop plugged in, it should read close to 100 percent.

    Checking Battery Charge with a Multimeter

    Step 1

    Fully charge your laptop battery.

    Step 2

    Turn off your computer and remove the battery. Look for a voltage rating printed on the battery. This will be the number to compare with your multimeter reading. Many laptops have voltages of 9.6V, 10.8V, 11.1V, 14.4V or 14.8V. Some have lower or higher ratings.

    Step 3

    Look for the connector where the battery interfaces with the computer. It will be near the center of the side of the battery that faces the computer when plugged in. Roughly an inch in length, it should resemble a series of at least five very narrow, identical slots that looks a little bit like your laptop’s exhaust fan grating, except smaller. The outermost of these slots will be the positive and negative terminals of the battery.

    Step 4

    Turn on your multimeter and set it to measure direct current voltage on the 20-volt scale (or anything close to 20 volts). Voltage settings are indicated by the letter “V” and direct current voltage settings are indicated by straight lines near the V, as opposed to wavy lines for alternating current.

    Step 5

    Insert one prong of your multimeter into the outermost slot on one end of the battery connector. Insert the other prong of your multimeter into the other outermost slot on the connector. It doesn’t matter if you match your positives and negatives. If you get them backward, it will just change the sign of the voltage, not the actual number, and the number is what’s important. Make sure each prong is touching bare, exposed metal.

    Step 6

    Observe the reading on your multimeter. A fully charged, healthy laptop battery will measure very close to the printed value on the battery.

    Step 7

    Try measuring your battery’s voltage after a 60- to 80-percent discharge, to get a comparison against the full charge value. A depleted laptop battery won’t measure anything close to 0V. There will still be several volts in it. What happens is that, once the battery drops below a certain voltage, your computer automatically shuts down. This is because if the voltage drops too low the battery will become damaged. Protective circuitry in the battery will then make it impossible for you to use a dead battery.

    Checking Battery Overall Health

    Step 1

    Fully charge your laptop battery.

    Step 2

    Turn on your computer, unplug it from the power outlet and run on the battery only.

    Step 3

    Get a sense of how fast the battery is draining. A healthy battery should last roughly as many hours as it says on the package. An unhealthy battery will drain much faster. Don’t drain the battery all the way for this test, but about halfway instead. Once your battery drains too fast for you to get practical use out of it, it’s time to get a new one.

    Tips

    • Most laptops have a battery meter in the icon tray in the bottom right corner of your Windows session. Look for an icon shaped like a battery or, if you have your computer plugged into power, an icon of a battery with a power plug. By hovering your mouse over the icon, you can also see how much battery power you have remaining, both as a percentage of total power and sometimes also as an estimate of how many minutes of power you have left. This is faster than checking battery power in Windows Mobility Center.
    • The company that produced your laptop -- such as Toshiba, Dell, Sony or Acer --also produced software that will tell you all about the condition of your laptop, including the charge level and overall health of your battery. If you bought your laptop with Windows preinstalled, then this software is already installed too. You might also have gotten an installation CD containing the software when you bought your computer. Check your computer’s user manual and the software that came with it.
    • Run your computer on battery at least once a week, draining it to between 40 and 60 percent of total power. These “exercise” sessions help the battery’s chemistry remain efficient longer, which means a longer battery lifespan. Don’t drain more than 40 to 60 percent if you can help it, as draining too much will begin to shorten your battery’s lifespan. However, do drain your battery completely once or twice a year. This will recalibrate the charge meter so that you continue to get accurate charge information.

    Required Items

    • Multimeter

    About the Author

    Josh Fredman is a freelance pen-for-hire and Web developer living in Seattle. He attended the University of Washington, studying engineering, and worked in logistics, health care and newspapers before deciding to go to work for himself.

    Photo Credits

    • Justin Sullivan/Getty Images News/Getty Images