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Comment by Reason077 | Hacker News Reader

I have an M1 MacBook Air and use an app called CoconutBattery to monitor power usage.

What I’ve noticed is that while the laptop is usually super efficient (say, 2.5-4W while web browsing giving 8+ hours battery life), occasionally the power draw climbs up to 6, 7, 8W or more with no obvious explanation, draining the battery in 3 or 4 hours.

Activity Monitor will show no apps using unusual energy yet the power is going somewhere? I’m suspicious that there’s something with maybe the WiFi hardware or the SSD which sometimes causes elevated power use, unseen by Activity Monitor?

Even a reboot won’t solve the phantom power drain while it’s happening, but it does seem to go away on its own eventually…

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Watch your backlight level, which auto adjusts to the room light level.

"When comparing battery life, remember that screen brightness makes a huge difference!

On an M1 MacBook Air sitting idle on the KDE desktop, you will get around 7 hours of runtime at 100% brightness, and 23 hours of runtime at the minimum (not zero) brightness.

Even keyboard brightness matters! Those numbers are with the keyboard backlight turned off. If you turn it on at max, even with the screen left at minimum, your runtime goes from 23 hours down to just 14 hours.

So please don't ask us what battery lifetime to expect while doing a certain task and expect a single answer!"

https://social.treehouse.systems/@AsahiLinux/110548137464042...

Yes, I should have mentioned I always have keyboard backlight turned off [1]

I’ve suspected something to do with screen brightness in the past also. System log was often full of messages from the brightness adjustment/monitoring daemon, which raised my suspicions, but I think it might just have been normal behaviour at the time.

However the mystery power draw seems to happen independent of screen backlight setting. ie: when the problem is happening, turning backlight right down will reduce power draw a bit, but it’ll still be high. On other occasions, even with the screen brightness at 100% I’ll still get “normal” power draw. I’ve experimented with turning off brightness auto-adjustment too, with no effect.

[1] Keyboard backlight is very annoying at night when trying to watch a movie or something, and Apple made it difficult to toggle on and off on recent Macs by removing the hot key for it. So I’ve learned to just live without it.

Keyboard brightness - you can put the control into control center and then it’s two clicks to get to a slider for it.

Not awesome, but for the relatively rare times I want to change it manually, it’s been acceptable.

Yeah I do have that, but I usually find it too slow/annoying to have to use the mouse to turn it on and off. It was so much quicker and easier when there was an F-key to instantly do it.

Maybe one day I’ll get around to making an app to map it to an F-key again, which has been on my todo list for a long time…

Have you got the automatic adjustment off? The night time thing hadn't bothered me.

https://support.apple.com/en-au/guide/mac-help/mchlp2265/mac

You are correct. Even plugging in my gaming mechanical keyboard makes a noticeable difference.

Metadata indexing for Spotlight?

I've had very stubborn runs of the md* indexer (not at laptop can't recall name -- mdimport?) decide that yes, this coffee shop is a great place to crank it up.

A similar one is a large initial indexing by the Dropbox app. I've had my M1 Air on the desktop Thunderbolt dock for the past month so it's gotten way past that initialization stage.

Spotlight’s energy use shows up in Activity Monitor, though.

Whatever drains my battery is invisible to Activity Monitor (but visible to apps that monitor the power management hardware itself), so presumably it must be some hardware device?

I'm no expert but I definitely can't help but wonder if it's WiFi or Bluetooth. Maybe something like radio interference making it work 50x harder?

Around a decade ago I had a MacBook that was super sensitive to interference issues. Although I'm not sure if that results in a big power draw (the way it does with cell phones for example when you're constantly going in and out of service).

I can fairly confidently rule out Bluetooth, as turning it off in control Center doesn’t seem to affect the power drain. Wifi is certainly a possibility though.

On my (2020 intel) MBP, SSD IO is VERY power hungry. Usually the culprit is Firefox, but my company is on the MS office suite, so sometimes it’s Outlook or Teams. It’s frustrating.

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