How does the browser read my battery level?
We call navigator.getBattery(), which returns a BatteryManager object with level (0-1), charging state, chargingTime, and dischargingTime. The values come straight from the OS power subsystem, so accuracy matches what your system tray shows. We also subscribe to change events, so the readings update the moment you plug or unplug the charger.
Why does the Battery Status API not work in my browser?
Firefox and Safari removed the Battery Status API in 2016-2017 because researchers showed it could be used for fingerprinting (the precise level and chargingTime form a quasi-unique ID). Only Chromium-based browsers (Chrome, Edge, Opera, Brave, Samsung Internet, Android WebView) still expose it. On unsupported browsers we show a notice — your battery is fine, the API is just blocked.
How accurate is the time-remaining estimate?
The OS-provided dischargingTime is an instantaneous projection — it assumes current power draw stays constant. Open a video or game and the figure can halve within seconds. Our optional discharge probe instead samples your level over 3 minutes and extrapolates linearly, which is more stable but still rough on devices where the kernel only updates the level in 5% increments.
What is a healthy discharge rate?
Idle laptops should lose 3-6% per hour with the screen on. Phones idle around 1-2% per hour with the screen off, or 8-15% per hour during light browsing. If you see double-digit drain at idle, check for runaway background apps or a swollen battery. A new laptop dropping below 80% design capacity within 12 months may qualify for warranty replacement.
Will running this test damage my battery?
No. Reading status is a passive operation with zero impact. The 3-minute discharge probe just watches the level — it does not artificially drain power. If you want to measure load discharge, run the CPU benchmark in another tab simultaneously and watch how the projection changes. That cross-test reveals how much runtime your workload actually costs.
What related tools should I check next?
Pair this with the CPU stress test and the WebGL GPU benchmark to see how full-load workloads translate into watts and projected runtime. The Sensors motion tool can confirm your device is not thermal-throttling under that load, which would inflate idle drain numbers afterwards.