Why is my Mac battery draining so fast?

You unplugged the MacBook with 90% battery and an hour later it’s at 60%. Either the battery is failing, or something is using more power than it should. Almost always it’s the second one.

Where battery actually goes

In rough order of impact on a typical MacBook: the display backlight, the CPU/GPU package, the wireless radios, and external peripherals drawing bus power. Background processes burn battery via the CPU. A hung daemon at 100% on one core can halve battery life without you noticing in the menubar percentage.

How to find the cause

1. Open Activity Monitor's Energy tab. Sort by "Energy Impact" (last 12 hours). The top of the list is your suspect.
2. Check what's running invisibly. Filter by "App Nap" and look at processes you didn't launch — helpers, daemons, sync agents.
3. Run pmset -g batt to see current battery state, draw rate, and whether anything is preventing sleep.
4. Check assertions. Run pmset -g assertions — these are processes telling macOS "do not sleep." A bad assertion is a battery killer.
5. Look at the display. Brightness at 100% with an external monitor connected can double your draw. Drop brightness and see if the rate changes.

The classic culprits

Chrome with many tabs, Zoom or Teams running in the background, a stuck Spotlight reindex, a Time Machine that’s been trying to back up for hours, photo library analysis (photoanalysisd), or a development tool like Docker that’s keeping CPU pegged. On Apple Silicon, anything forcing the chip out of its low-power state is expensive — even small amounts of background work prevent the deep idle states that make M-series battery life so good.

Reading the draw rate

The number to watch is wattage. A MacBook Air at idle draws 3-5W. Light browsing — 6-10W. Video call — 12-18W. Sustained heavy work — 20-30W+. Run sudo powermetrics —samplers cpu_power -i 1000 -n 5 to see actual package power. If you’re idle and the chip is pulling 15W, something is wrong.

Watching power live

The battery percentage in the menubar doesn’t tell you the draw rate, which is the actual signal. Beacon shows live power draw in watts alongside CPU load and temperature — when battery drops faster than expected, the wattage tells you why immediately. $14.99 lifetime. Download Beacon if you want it on screen.

Battery health vs battery drain

If draw is normal but battery percentage drops fast anyway, check battery health: System Settings - Battery - Battery Health. A cycle count over 1000 or a “Service Recommended” warning means the cell is degraded and no amount of process-killing will fix it.