How this battery test works
The page reads your battery through the browser's Battery Status API and shows the level, whether the device is charging, the estimated time to full or time to empty, and updates live as the values change. Plug in or unplug the charger and watch the numbers react. Everything stays in your browser and nothing is uploaded.
This API exists in Chrome, Edge and Opera on desktop and Android. Safari and Firefox do not support it, because it can be used to fingerprint visitors. If you see "not supported," that is the browser's decision, not a fault in your device. Desktop computers without a battery also report nothing useful.
We deliberately do not show a battery "health" percentage. Browsers cannot read it, and any website that claims to is guessing. The steps below show the real number.
How to read the results
- Level. The current charge in percent.
- Charging state. Charging, discharging or full. A battery stuck at "charging" with a falling level means the charger is too weak for what the device is doing.
- Time to full or empty. An estimate that can jump around, especially right after unplugging, and sometimes shows "calculating" or infinity.
- Live updates. A level that drops quickly with light use, or jumps from 30 percent to 5 percent, points to a worn battery.
Battery draining fast? Check real health with these steps
- Windows. Open a terminal and run
powercfg /batteryreport. Open the HTML file it creates and compare Design capacity with Full charge capacity. - macOS. Go to Apple menu → System Settings → Battery → Battery Health, or hold Option and click the Apple menu, then System Information → Power to see Cycle Count and Condition.
- Android. Many phones show it in Settings → Battery or Settings → About phone → Battery information. On others, dial the manufacturer's service code or use the maker's app.
- iPhone. Open Settings → Battery → Battery Health & Charging and check Maximum Capacity.
- Cycle counts. One cycle equals using 100 percent of capacity in total, not necessarily in one go. Most laptop and phone batteries keep about 80 percent capacity after several hundred full cycles.
Why test your battery
Heat is the biggest enemy of lithium-ion batteries, followed by sitting at 100 percent or 0 percent for long periods, and fast charging in hot conditions. Checking the battery before you buy a used laptop or phone, or when runtime suddenly drops, tells you whether the battery needs replacing. Keeping charge between about 20 and 80 percent, avoiding heat, and using the original charger will slow wear.
A final tip: do not trust a single reading. Check the level a few times over an hour of normal use, and if it falls much faster than it used to, run the health check for your system above before deciding to buy a replacement.
Frequently asked questions
Why does the battery test not work in Safari or Firefox?
Those browsers do not support the Battery Status API because it can be used to track people. Use Chrome or Edge on desktop or Android instead.
How do I check battery health on Windows?
Open a terminal and run powercfg /batteryreport. The generated report lists design capacity and full charge capacity, which show how much the battery has worn.
How do I check battery health on an iPhone?
Go to Settings, Battery, Battery Health & Charging. The Maximum Capacity percentage compares your battery to when it was new.
Is this tool showing my battery health percentage?
No. Browsers cannot read it, so we show only level, charging state and time estimates, and point you to the real tools on each system.
What is a battery cycle?
One cycle is a total of 100 percent discharge, which can be spread over several days. Batteries are usually rated for several hundred cycles before capacity drops to about 80 percent.
Why does the time remaining keep changing?
It is an estimate based on current power use, so it changes when you open apps, change brightness or plug in a charger.
What is a normal battery drain rate?
It depends on the device and use, but a phone idling usually loses only a few percent per hour, while gaming or video can use 15 to 25 percent per hour. A laptop usually drains faster under load and slower when idle.
What is the 20–80 percent charging rule?
Lithium-ion batteries age less when they stay between about 20 and 80 percent charge than when they are often fully charged or fully drained. It is a guideline to slow wear, and it is fine to charge to 100 percent when you need the runtime.