Battery Readout
Your device's charge level, charging state and estimated time remaining, read straight from the browser. Nothing is uploaded — and if your browser does not offer this, the page will say so plainly rather than showing you an empty panel.
Not available in this browser
Nothing is wrong with your battery or your device — the reading simply is not offered to web pages here. To see it, open your operating system's own battery information: System Settings → Battery on macOS (hold Option and click the Apple menu → System Information → Power for cycle count and condition), Settings → System → Power & battery on Windows, or Settings → Battery on Android and iOS.
Or try this page in Chrome, Edge, Opera or Samsung Internet, which do expose it over an https connection.
What this reads, and what it cannot
This page uses the browser's Battery Status API, which reports four things: the current charge level, whether the device is plugged in, and the estimated time until the battery is full or empty. Those estimates come from the operating system and are exactly as reliable as the ones in your system tray — they swing about after a change in load, and settle once your usage does.
It cannot tell you your battery's health, and it is worth being plain about that because "battery health" is what most people are looking for when they land here. Health means the ratio of what the battery can hold now to what it could hold when new, and calculating it needs the design capacity and the cycle count — figures the operating system keeps and does not hand to web pages. A battery worn down to 60% of its original capacity still reads 100% here when it is full, because it is full for what it is now. For the real figure: on macOS hold Option, click the Apple menu, then System Information → Power, and read Cycle Count and Condition; on Windows run powercfg /batteryreport in a terminal and compare Design Capacity with Full Charge Capacity; on iPhone open Settings → Battery → Battery Health.
Why some browsers refuse
Because the reading identifies you. A battery level expressed to two decimal places, combined with the time remaining, is close to a unique number that persists for as long as it takes to charge or discharge — enough to link two visits that had nothing else in common. Firefox removed the API from web pages in 2016 for exactly that reason, Safari has never shipped it, and Chrome only offers it over a secure connection. That is a deliberate privacy decision by browser makers, and this page will simply tell you so rather than pretending to have a reading.
Making a battery last
The single biggest factor in how fast a lithium-ion battery wears out is heat, followed by the amount of time it spends sitting at a very high or very low charge. Leaving a laptop plugged in at 100% all day, every day, ages it faster than using it — which is why most manufacturers now ship an optimised or limited charging mode that holds it near 80%. Use it if you have it. A rough figure for a phone or laptop battery is 500 to 1000 full cycles before it drops to around 80% of its original capacity, which is typically two to four years of ordinary use.
Nothing on this page is recorded or sent anywhere; the reading is drawn locally and stays in your browser. See also common hardware faults and how to diagnose them.
