Which apps drain a Mac's battery

Name: WattMate
Price: 9.99 USD

Updated 23 August 2026 · every figure below is measured on two Apple silicon Macs and links to the page where the run is written out in full. Who measures this.

Activity Monitor gives each app an "Energy Impact" score with no unit. These are watts, measured on battery, across thousands of ten-second windows — and the spread between apps turns out to be about four hundredfold.

The measured cost, side by side

App	Typical power while running	Busiest window seen	Windows measured
Chrome	2.3 W · 4.1 W	24.5 W	205 of 217 · 157 of 157
Xcode	3.7 W	48.5 W	217 of 217
Telegram	0.29 W · 0.26 W	see the page	157 of 157 · 339 of 339
Spotify	0.19 W · 0.03 W	see the page	110 of 217 · 157 of 157
Slack	0.01 W	see the page	153 of 157 · 173 of 339

Two figures where there are two: the same app on two different Macs, because the answer is not a property of the app alone. Chrome costs almost twice as much on the quiet machine as on the busy one — not because it works harder there, but because on a quiet Mac there is less else competing for the same watts.

The popular suspect is innocent

Ask which app is eating a Mac's battery and the usual answers are Slack and Chrome, in that order. Measured, Slack sits at 0.01 W — the smallest number in the table, roughly a twenty-sixth of Telegram and a four hundredth of Chrome on the same machine. Quitting it gives back minutes you would not notice in a working day.

Chrome is a real cost. But even there, the arithmetic almost everyone runs is wrong: you cannot subtract an app's watts from the machine's and call the remainder savings, because the screen and simply being awake do not go away when the app does. On the quiet Mac that subtraction broke in 117 of 157 windows — three quarters of the time.

The one that is worth quitting

Xcode is the clearest case in the set: a typical 3.7 W, a middle half spanning 1.7 to 13.0 W, and a busiest window of 48.5 W. It is the only app here whose peak is bigger than most Macs' entire draw. If a build is running, that is where the charge is going — and the page has the full 217-window run.

Questions people ask

Which app drains a MacBook battery the most?

Of the five measured here, Xcode: a typical 3.7 W and a busiest window of 48.5 W, which is larger than most Macs draw in total. Chrome is second at 2.3–4.1 W depending on the machine. But the honest answer for your Mac is your own list — the same app costs almost twice as much on a quiet machine as on a busy one.

Does Slack drain a Mac's battery?

Measured across 153 of 157 windows on one Mac and 173 of 339 on another, Slack sat at 0.01 W — the cheapest app in the set, and roughly a four hundredth of Chrome on the same machine. It is the most frequently accused app in this category and the least deserving of it.

Why does Activity Monitor show nothing when the fan is loud?

Energy Impact is a relative score with no unit, sampled when you open the window. The app that spiked two minutes ago is no longer there to see. Watts measured over continuous ten-second windows keep the history the score throws away.

Can macOS tell which app used the GPU?

No. macOS has a total for graphics energy but no per-app counter for it, so any split between apps — ours included — is inferred from how long each app kept the GPU busy. The total is exact; the split is not, and we say so on every page.

Why per-app watts are hard, and who can print them

Chrome holds a median of 16 processes on one Mac and 19 on the other, peaking at 40 — renderers, GPU helpers, the network service, each its own line in Activity Monitor. A tool that samples once a second misses everything that lived and died in between. WattMate credits that energy back through kernel resource coalitions, which is why its Chrome row is one number instead of forty.

Graphics is the honest limit: macOS has a total for GPU energy but no owner for it, so the split between apps is inferred from GPU time, not measured. That is stated on every page rather than hidden — the full method, and where it stops, is in how we count.

What to do with a number like this

A watt figure alone still does not answer the question people actually have, which is how much longer the charge would last. WattMate names that in minutes before you quit anything, then measures the Mac again two minutes after you do and prints what really changed — or says plainly that the effect could not be isolated. That re-measurement is the part we have not found in any other Mac battery app.