A Mac may feel slower, warmer or less efficient for a while after a major macOS update. Spotlight can rebuild its index, Photos may analyze a library, and cloud services can synchronize changes. That background work competes for processor time and battery, but it is only one possible explanation.
See what is using CPU and energy
Open Activity Monitor → CPU and sort by % CPU. If indexing or photo-analysis processes are busy shortly after an update, let the Mac finish its work while connected to power and on a stable surface. Check the Energy tab for apps using a lot of energy during ordinary use.
Do not force-quit system indexing processes to make them stop. macOS may start them again, and the work may take longer. If one app stays busy when you are not using it, quit it normally, update it, or check with its developer.
Check the usual causes of overnight battery drain
- Cloud sync, backups or downloads that are still active.
- Browser tabs or media apps keeping the Mac awake.
- Login items or background helpers that relaunched after the update.
- External devices or displays drawing power or preventing sleep.
For a laptop, review System Settings → Battery and Activity Monitor. If the battery drains while the Mac should be asleep, first disconnect nonessential accessories and check which apps are active. Change one thing at a time so you can tell what helped.
Give indexing time, then reassess
There is no universal number of hours for post-update work to finish: library size, network speed and how often the Mac is idle all matter. Let it run plugged in for a few quiet periods, then compare battery use under similar conditions. If high CPU, heat or fast drain continues during light use after background tasks settle, investigate apps, battery condition or hardware support instead of assuming it is still indexing.
Apple references
- Mac laptop operating temperatures
- Activity Monitor User Guide
- If your Mac battery runs out of charge quickly
Reviewed September 28, 2026. This guide links to Apple Support for platform instructions.