Activity Monitor’s Energy Impact is a relative indicator for comparing apps. It is not a watt meter or an app-specific battery percentage. Apple distinguishes the current Energy Impact from 12 hr Power, an average over the last 12 hours or since startup. Neither is a remaining-runtime estimate. Apple guide

Conceptual comparison of a current relative energy indicator and a historical average

Conceptual illustration, not a macOS screenshot or measurement.

Current impact and the 12-hour average

Apple describes Energy Impact as a relative measure of an app’s current energy use. The 12 hr Power column is the average Energy Impact over the previous 12 hours, or since the Mac started. It is not cumulative watt-hours and does not estimate remaining battery time. Interpret the values with the app’s workload and observation window in mind. Apple guide

Expert perspective: a score does not diagnose the cause

A high value can help identify an app to investigate, but it does not by itself mean the app is misbehaving. Apple’s developer guidance discusses energy impact alongside app activity such as CPU work. Apple does not provide a simple public formula for converting the score to watts, so do not assign unsupported fixed CPU, GPU, network, or disk weights. Mozilla engineer Nicholas Nethercote also noted that the metric’s precise meaning was unclear. The indicator remains useful as a relative clue, with those limits. Apple Developer Nethercote

Investigate without losing work

Check whether a high ranking persists and what the app is doing at the time. Save your work; if the app responds, try Quit first. Apple documents Force Quit for an unresponsive app or process. Force Quit can discard unsaved changes, and closing an app does not guarantee a specific battery-life improvement. Also consider display brightness, connected devices, charging state, and background work. Apple quit guide

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