Battery draining after the macOS 27 update?

Updated 11 November 2026 · Who measures this.

Some extra battery use is normal for the first 1 or 2 days. Spotlight re-indexes the disk and caches are rebuilt, and that cost should shrink day by day. If the battery is still worse after 3 days, it is unlikely to be the rebuild: look for what else changed, most often an app that got more expensive.

macOS 27, Golden Gate, shipped on 14 September 2026. It is the first macOS for Apple silicon only.

How do you tell whether the update is to blame?

Watch whether the cost shrinks. The rebuild is real work and it ends, so it fades day by day. An app that got more expensive stays where it is.

Activity Monitor can't answer this: it keeps no more than a 12-hour average, and Energy Impact is a number without a unit, which Apple's own documentation calls a relative measure. WattMate measures power by app in watts and keeps its measurements, so "this app got more expensive after the update" is a check, not a feeling. If you installed it only after updating, you won't have the before, but you will have today against tomorrow.

When an app stays expensive, quit it while on battery. WattMate re-measures the Mac a couple of minutes later and prints what changed, or says that the effect couldn't be isolated.

For the nights, macOS keeps a power log of every wake-up and, most of the time, the name of the service that asked for it. The direct download of WattMate reads that log; the App Store edition can't. On the Mac we measured on macOS 26, half of the total wake time belonged to Spotlight, the indexer.

Why is the battery worse right after an update?

Because the system rebuilds itself. Spotlight indexes again after a software update or upgrade, which Apple says can take hours or even days. Caches are rebuilt too, and apps may redo work such as compiling shaders on first launch. This is real energy used on real work, and it ends.

What if it isn't the update at all?

Then an app, the battery or your workload is the cause, and the list of apps in watts settles it faster than a forum thread does.

• An app shipped its own update the same week. The timing points at Apple, the watts point at the app.
• Battery age picked this month to show. Health is a slow curve, but people check it right after updates, so updates get the blame.
• The workload changed: a new project, a new call app, an external display.

Does macOS 27 itself use more power?

Our 2 lab Macs show no sign of it at rest, but we have no clean before and after: no Mac ran the same lab test on 2 versions of macOS. The closest we have is a pair of 14-inch MacBook Pros with the same M1 Pro chip, one on macOS 14.2.1 and one on 27.0.1, put through the same steps.

At rest the 2 are 0.15 W apart, and under load the gap goes both ways. The 2.1 W at 4 cores repeated in both runs, but these are 2 separate Macs, so we can't say macOS caused it. The 64 Wi-Fi wake-ups were 1 night: the night before, that Mac had none.

One Mac does have a before and after, from everyday use rather than a test. A second Mac that stayed on macOS 26.3 shows the same weeks with no update.

The work on the M3 Max changed too, so this cannot isolate what the update did. It shows no large increase on that Mac, and it does not show that macOS 27 saves power.

What changed underneath in macOS 27?

On the M3 Max we updated, 2 things: the chip's CPU energy counters update in bursts, and the battery's capacity and temperature readings moved to a new place in the I/O Registry, the system's list of hardware. Both affect any app that reads those counters or readings, ours included.

The chip's CPU energy counters now update in bursts. On our Mac, macOS 26 updated them continuously, and macOS 27 moves them a few minutes apart; other chips we have not checked. The counter sat still through a 3-minute probe, and between 2 readings 3.7 minutes apart it jumped by 768 joules at once, about 3.4 W of average draw over that gap. An app that splits power from those counters every few seconds now gets lumps instead of a stream. The graphics counter still advances every few seconds.

WattMate spreads each burst over the minutes since the previous one, by how much the apps worked, so "Background work" and the Neural Engine show up a few minutes late; the Measurements page says so. Per-app watts, the total draw, the quit check and the receipt do not wait for the bursts: each app's own work comes from its per-process energy counter, and the total draw comes once a second from the Mac's system management controller.

The battery's readings moved. The capacity readings and the temperature went to a child entry, AppleSmartBatteryPack, under the battery's own entry AppleSmartBattery. WattMate 1.3 lost its battery health page on macOS 27 and ended every quit with "couldn't isolate the effect"; 1.3.1 reads the new layout.

Questions people ask

Is it normal for the battery to be worse right after updating?

For the first 1 or 2 days, partly. The system rebuilds indexes and caches, and that work is paid for in battery. It should visibly shrink day by day. Worse and staying worse after 3 days is unlikely to be the rebuild.

Should I quit apps to save battery after the update?

Only the ones that measurably matter. Most apps cost close to nothing in the background, and quitting them buys you nothing back. Measure first: quit the one expensive row, not everything, and check what the quit returned.

Does a beta use more battery?

The rebuild may run again after each beta you install. A logging profile from Apple's Profiles and Logs page, installed for a bug report, turns on extra logging, so if you are not filing reports, remove it. We couldn't find an Apple statement that betas use more battery in general, and we haven't measured it.

Does WattMate work on macOS 27?

Yes, from 1.3.1. Versions 1.3 and earlier run on macOS 27 but show no battery health page and end every quit with "couldn't isolate the effect". Since 1.5 the temperature row and the measured health are back in the statistics window too. WattMate requires macOS 14 or later on Apple silicon.

How it was measured

What this doesn't show

• A clean before and after. No Mac ran the same lab test on 2 versions of macOS, so we have no figure for what macOS 27 costs overnight or per day. If a page tells you how many watts macOS 27 costs, ask where the number came from.
• What the rebuild costs. The lab Macs run with Spotlight and automatic updates off.
• The price of a single overnight wake-up. The battery publishes its charge reading only about once a minute, the reading wobbles and it bounces back after a wake. We say how often the Mac woke and for how long.

Related: where the charge goes with the lid closed · what "using significant energy" actually means · why the percentage jumps and drops · all the guides