What is the Battery Status API?

The Battery Status API was a web API that let JavaScript read a device’s battery level, charging state, and rough time-to-charge or time-to-empty estimates via navigator.getBattery() and a BatteryManager object. It was meant for power-aware sites (for example, reducing motion when charge is low). Major browsers have removed or restricted it because fine-grained battery readouts became a tracking risk.

How it worked before removal

Calling getBattery() returned a Promise that resolved to BatteryManager with level (0.0 to 1.0), charging, chargingTime, and dischargingTime. Event listeners could react to levelchange and related events.

Research showed that precise level plus charging could act as a short-lived fingerprint: few users share the exact same percentage and plug state at the same instant. That enabled cross-site correlation even when cookies were cleared, which conflicted with privacy expectations.

Vendors responded by deprecating or gating the API. New sites should not rely on it. For performance, prefer general optimizations (smaller assets, less main-thread work) and user-controlled modes such as data-saver hints where appropriate.

Why it mattered for fraud and fingerprinting

Fraud vendors and trackers sometimes folded battery signals into browser fingerprint bundles alongside canvas, audio, fonts, and WebRTC. Stable or synchronized battery tuples across many sessions could indicate shared virtual profiles or scripted environments, though the signal was noisy and short-lived.

Today, with the API largely gone, historical knowledge still explains old datasets and why some legacy scripts fail silently. Current fraud detection leans on durable signals: IP and ASN reputation, proxy and VPN hints, device integrity, and behavior around clicks and forms. Understanding removed APIs clarifies why modern stacks emphasize other layers for click fraud and ad fraud. Privacy-focused discussion of fingerprinting overlaps with topics like third-party cookies and evolving browser limits.