How to use the battery test
- Battery level and power state: Shown immediately when the page opens.
- Time remaining or time to charge: Estimated from how fast the level is changing. It needs a few percent of change, so it starts as 'Calculating...'.
- Full battery life: How long a full charge would last at your current usage, worked out while running on battery. It keeps the last value while you're charging.
- Battery % trend: The chart adds a point every time the level changes.
For the best estimate, unplug the charger and leave the page open while you use the device normally. The longer it runs, the more accurate it gets.
Checking battery health
- Short full battery life: If the full battery life estimate is far below what the device lasted when new, the battery has likely worn down. Batteries lose capacity with every charge cycle.
- Sudden drops: A level that jumps down several percent at once, or a device that shuts off with charge remaining, often means the battery is failing.
- Not charging: If the state says 'Charging' but the level doesn't rise, the charger may be too weak or the cable faulty.
- Detailed report (Windows): Run 'powercfg /batteryreport' in Command Prompt for the battery's design capacity versus its current full charge capacity.
- Detailed report (macOS): Open System Settings → Battery for the battery's condition, or System Information → Power for its cycle count.
Common Issues & Fixes
It says the Battery Status API isn't available
- Browser: Firefox and Safari don't provide battery information to websites. Open this page in Chrome, Edge, or Opera.
- Desktop computers: Desktops without a battery may report a full battery that is always charging.
The estimates stay on 'Calculating...'
- Give it time: Battery level only changes in 1% steps, so estimates need several minutes of readings.
- Unplug: The full battery life estimate only updates while running on battery.
Use this battery test to see how your battery is really holding up, without installing anything.
Frequently asked questions
How accurate are the estimates?
They're based on how fast your battery level changes while the page is open, so they reflect your current usage. Heavier use drains faster and shortens the estimate.
Why doesn't this work in Firefox or Safari?
Those browsers removed battery information for websites to protect privacy.