Does Slack drain your Mac's battery?

Measured 15 August 2026 · 153 windows on one Apple silicon MacBook · reproducible with the script at the bottom

Short answer: almost never — and then, briefly, quite a lot. Slack has a reputation as a battery hog, and the reputation is built on the minutes it deserves rather than the hours it doesn't.

The gap between typical and worst is 736-fold. Half the time Slack cost less than a hundredth of a watt — on a 60 Wh battery that is, quite literally, days of runtime before it adds up to one percent. Then in a handful of windows it reached 7.4 W, which is more than the entire rest of that Mac was using at idle.

So which one is "the truth"?

Both, and that's the point. An app with a spiky profile is invisible in averages and unmistakable in the moment. If you looked at Slack during one of those spikes you'd conclude it was eating your battery; if you looked at any of the other 150 windows you'd conclude it does nothing. Neither snapshot is wrong; both are useless on their own.

What we deliberately can't tell you is why the spikes happened. The log records what each app used, not what you were doing — so "it was a huddle" would be a guess, and a plausible guess is still a guess. What we can say is that they were brief and rare, which is why the total across the whole period is barely over one watt-hour.

What this means for your afternoon

If your battery is disappearing and Slack is open, Slack is probably not the reason — and quitting it will most likely return you nothing, while costing you the messages. On the same machine, over the same period, Chrome was using around four watts as a matter of routine: that page has the numbers.

The useful move isn't to quit the app with the worst reputation. It's to look at what your Mac is using right now, in watts, and quit whatever is actually at the top — which on most machines is a browser, an editor or a video call, not a chat client sitting in the background.

What this does and doesn't prove

One Mac, one workspace. Slack appears in only one of the two databases behind these pages, so unlike our Chrome page there is no second machine to disagree with it. A Mac in busier workspaces, with more calls or more open channels, would spike more often. Treat the shape — near-zero with rare spikes — as the finding, and the exact figures as one example of it.

The spikes are real and we are not smoothing them away. It would be easy to publish just the median and call Slack free; the 7.4 W window happened, and an app that occasionally costs that much on battery deserves to be seen when it does. That is what a live measurement is for.

Measure your own

Every figure here comes from one script over WattMate's own database:

python3 Scripts/app-energy-report.py <database> Slack

Or watch it live: the trial ranks every app by actual watts and tells you what quitting the top one is worth — then checks its own answer two minutes later.

Related: what Chrome costs · what Spotify costs · does quitting apps help at all?