Used Laptop? Check the Battery in 2 Minutes, Free

The most worn-out part of a used laptop is usually the one you cannot see from the outside: the battery. The good news is that both Windows and Mac laptops will tell you how worn it is, for free, in about two minutes. You do not need to install anything. You only need to know which two numbers to look at.

Screen and keyboard are easy to judge by eye. The battery needs a number, and the laptop will give it to you.

Why the battery is the part to check first

A laptop battery is a consumable part. Every full discharge and recharge uses a little of its life, and a battery that has done a lot of cycles holds less charge than it did when new. A used laptop with a flawless screen can still die in a short time once you unplug it. Checking takes less time than testing the keyboard, so do it before anything else.

Apple's own support page puts a number on the wear. Apple says its Mac laptop batteries are designed to keep up to 80% of their original charge capacity when they reach their maximum cycle count, and it recommends replacing the battery at that point for best performance. The same page says a battery can still be used past that count, but you may notice shorter battery life. That is a useful way to think about any laptop: the cycle count is not a cliff, it is a slow slope.

What a "cycle" really is

A cycle is not one plug-in. Apple explains that a cycle is complete when you have used an amount of charge equal to the battery's full capacity, but not necessarily all at once. Use half the charge today, recharge, use half tomorrow, and that adds up to one cycle, not two. So a laptop that lived on a desk plugged in can have a low count, and one that was run flat daily can have a high one.

Windows: run one command

Microsoft documents a built-in tool called powercfg. Its battery report option generates a report of battery usage characteristics over the lifetime of the system, saved as an HTML file in the folder where you ran it. Steps:

1. Open Command Prompt or PowerShell on the laptop.
2. Type powercfg /batteryreport and press Enter.
3. Open the file it names in any browser.

Microsoft's page also lets you choose where the file is saved (/output followed by a file name). Look in the report for two capacity figures, usually labelled design capacity and full charge capacity. Design capacity is what the battery could hold when it was made. Full charge capacity is what it can hold today. Divide the second by the first, and you have the share of the original battery that is left. (Those labels come from how the report is commonly laid out; Microsoft's page only describes it as a report of battery usage characteristics, so if your report looks different, look for the closest equivalents.)

For example, a design capacity of 50,000 and a full charge capacity of 40,000 means 80% remains. Those numbers are made up for illustration; yours will be different. Because Microsoft describes the report as covering the lifetime of the system, it shows the history of the battery, not just a snapshot of today. That history is exactly what a seller's "it holds a charge fine" cannot show you.

Why bother with a report when you can simply watch the battery icon? Because the icon only tells you how full the battery is, not how large it is. A worn battery can show 100% and still run out in a fraction of the time a new one would. The report measures the size of the tank, which is the thing you are paying for.

Mac: four clicks

Apple's steps are short:

1. Hold the Option key and click the Apple menu.
2. Choose System Information.
3. Under Hardware, select Power.
4. Read the cycle count under Battery Information.

Then compare that number with the maximum for that model. Apple publishes a table. Its listing shows 1,000 cycles for most recent models, and lower limits of 500 and 300 for some of the oldest laptops, so look up the exact model on Apple's page rather than guessing. If the count is close to the limit, treat the battery as due for replacement.

How to read what you find

A middle number is a judgment call, and Microsoft and Apple do not publish a pass mark for a used laptop. The one firm line from Apple is the 80% design point at the maximum cycle count. The sensible rule of thumb is simple: the less of the original battery that is left, the less you should pay, because a worn battery means a repair bill or a laptop that only works near an outlet.

Check the software too: the Windows 10 date

Battery is not the only thing that wears out. Microsoft says support for Windows 10 ended on October 14, 2025, and that it no longer provides software updates, security fixes or technical help for Windows 10 PCs. Those computers keep working, but without regular security updates. Microsoft also describes a paid-or-points Extended Security Updates program that runs until October 12, 2027, with options including a one-time $30 purchase, 1,000 Microsoft Rewards points, or no extra cost if you sync your PC settings. So when you look at a used Windows laptop, open Settings and see which version it runs, and whether it can be upgraded to Windows 11. A cheap laptop stuck on Windows 10 has a deadline built in.

A 2-minute routine for any used laptop

1. Charge it fully and unplug it. A laptop that only works on the charger is telling you something.
2. Run the battery check above and write down the numbers.
3. Look up the model's recall status; our guide to a 5-minute recall test shows how.
4. Check the version of the operating system.
5. Reset it before you use it; see the factory reset checklist.
6. Plug something into every port and press every key.

Shopping locally, in DC, Maryland and Virginia

If you are buying in person around the DMV, ask to run the check on the spot. Any honest seller will let you spend two minutes on it, and you can compare prices before you commit. If you would rather shop online, browse our electronics and read each listing's condition notes and the help page for how buying works. You can also read our guide on how to win an auction without overpaying before you bid on something with a battery inside.

The bottom line

A used laptop's battery is the quickest thing to measure and one of the most expensive things to get wrong. On Windows, compare full charge capacity to design capacity. On a Mac, compare the cycle count with the model's limit. Then price the battery into the deal, and check the operating system's support date while you are there.

If this saved you a bad buy, send it to a friend who is shopping for a laptop.