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Live charge level, charging state, and how fast the battery is actually filling or draining — measured from real level changes while this page is open, next to the operating system's own estimate. Reads the browser's Battery API; nothing is installed and nothing leaves the device.
The measured rate is computed from the battery level's real movement while this page is open — each 1% step is timestamped, and the rate is the slope over the recent steps. It needs a few minutes (levels report in 1% increments, so a laptop draining 20%/hour steps only once every ~3 minutes). The system estimate is whatever your OS reports through the browser; some platforms expose it, many don't.
A healthy laptop battery idles at 5–15%/hour with the screen on and can exceed 100%/hour under full CPU+GPU load. If your measured drain at idle looks like someone else's under load, check for runaway background apps first — and then battery wear: an aged cell reports full percentages over a much smaller real capacity, so everything appears to drain faster.
The Battery Status API is supported in Chrome, Edge and other Chromium browsers. Firefox and Safari removed or never shipped it for privacy reasons — your OS battery indicator remains the reference there.
Two estimates are shown: the OS's own (when exposed) and one measured live from real level changes. The measured one needs a few minutes of steady use to converge, and any workload change changes it.
A page can't harm a battery — it can only use CPU/GPU while open. This test is nearly idle; to see drain under load, run the CPU or GPU stress test in another tab and watch the rate here.