Mac mini M4 auto turn on after power connected. It should have wait for the user to press the power button instead.

Apple  introduced a new Energy setting in macOS Tahoe 26.5 called “Start up when power is connected”, which explicitly controls whether supported Macs start when power is connected. The “Never” option is intended to require pressing the physical power button. Apple's official documentation explains this feature.

Since you've already tried all three options in Energy settings and the behaviour persists, I would treat this as a possible macOS/firmware regression rather than immediately assuming the hardware is faulty. However, the community reports don't prove that this is the cause of your particular issue.

Here's what I would do:

1. Confirm that Start up when power is connected is set to Never in System Settings → Energy.
2. Back up your Mac, install any newer official macOS update available, and test again.
3. Contact Apple Support and explain that the problem started after the OS update, persists with automatic startup disabled, and occurs every time power is restored. Ask them to check whether this is a known software or firmware issue.

If Apple cannot resolve it remotely, arrange a diagnostic at an Apple Store or an authorised service provider. You don't need to assume it is a hardware fault, but getting it checked is reasonable if the behaviour persists.

One other detail worth testing: after shutting down, wait at least 30 seconds before restoring power, as Apple recommends allowing the power supply to discharge. This is a useful test, not a guaranteed fix.

My M4 Mac Mini running macOS 27.0.1 does not Auto Start when electrically are restored  nor does my M6 Mac Mini also running macOS 27.0.1

Report the issue to Apple using Feedback links, but don't hold your breath for a fix in the next macOS update.

Feedback - Mac mini - Apple

Feedback - macOS - Apple

The Mac mini uses very little power idling with the display(s) off and almost nothing while in sleep mode.

Personally I would move the Mac mini to an un-switched outlet or leave the main power on for several reasons.

1) The Mac mini will have less problems and last longer if it is left on.

2) Repeated power cycling 365+ times a year is worse on the hardware than leaving it on.

3) The Mac mini has an internal POS coin battery, that will drain out more rapidly if the main power regularly turned off.

I have a feeling that I hit into your point 3 issue, that my coin battery has drain out.

when my Mac mini auto turn on, the clock reset at 12:00am. I suspect that’s the reason whatever setup I did is gone when I power off. Then macOS by default make it auto start before it read any macOS setting on the energy setting

I have a similar setup and it happens to my Macs too. 'Been that way for years & numerous versions of macOS. It has never caused a problem and I do not believe there's any reason to be concerned.

Also, I do not advise using any terminal commands in an attempt to change the behavior. You could end up causing more problems than it solves. Take reddit , AI & other stuff on the internet with a grain of salt ... meaning, be very very cautious about believing any of it.

skydiverock wrote:

I have a feeling that I hit into your point 3 issue, that my coin battery has drain out.

It would be highly unusual for the CMOS battery in a Mac mini M4 to already be bad. The M4 mini was only released 2 years ago and new ones are still available. How old is yours?

The battery can be replaced but you must open the case to do so. If your mini is covered by warranty or Applecare that would void the coverage.

If your mini is under warranty or Applecare, contact Apple Support.

Just adding my experience. YMMV ...

I have always shut down & powered off my Macs when not in use (powered off at the surge suppresor). That means at least overnight every night and sometimes during the day. Have never had any problems from doing so, not even with any HDDs. I do it for two reasons - 1) overall practice of minimizing electricity consumption that is of no use (it adds up) and 2) security (an unpowered computer isn't exposed). I also completely disconnect from power & network when thunderstorms are about.

In all my years of using & supporting Macs - hundreds of them - I have only ever needed to replace a CMOS battery twice - and both were old Macs that had been sitting unused for about 5 years. One was a 2004-era eMac, the other was an early (2007) aluminum iMac. Not one since.

In all my Mac years (1984 to date), the only Mac that ever really let me down was the display in a 4 year old Early 2006 Intel iMac.

I think your choice for over-night and longer times of none use is fine. The problem is that shutting down and killing the power doesn't work well if the Mac need to be used at all different times of the day and night. In other words, switching it on and starting it up can use as much or more power than just letting it idling or sleeping for a couple of hours.

The only time that I make any effort to disconnect them from the power and ethernet network, is during an occasional sever local thunderstorm.

den.thed wrote:

In all my Mac years (1984 to date), the only Mac that ever really let me down was the display in a 4 year old Early 2006 Intel iMac.

Just goes to show how well built Macs are.

The only Mac that ever "let me down" (and it wasn't a big letdown) was an iMac G5 whose display went bad just before its Applecare coverage was about to expire. I took it in to a Genius Bar immediately and the display got replaced at no charge. Happy camper!

Between that and an iPod Touch that went bad (also replaced at no charge under Applecare), I'm about even on the cost of Applecare coverages over the years vs. what those two repairs/replacements alone would have cost out of pocket.

The problem is that shutting down and killing the power doesn't work well if the Mac need to be used at all different times of the day and night.

Agreed!

Yea' the Late 2005 G5 and the Early 2006 Intel iMac's, used the same LG displays.

I unplugged the internal display, plopped an external display down in front of it and let the grandkids play games on it for a few more years.

My first Mac was a MacPlus with a whopping 1 MB of RAM. All the Macs I have had since then I only had two issues. On my dual processor space heater PowerMac G5, I had a video card go south which wasn't an Apple designed product (I don't recall whether it was an AMD or NVidea card). The other was a Seagate internal drive that went south in my late 2013 27" iMac, which I was planning to replace with a SATA SSD anyway. Its demise just sped up the process.

BTW, I still have a 2010 Mini I am using for a home server.

I used our 2010 Mac mini w/1T PNY SATA SSD upgrade as a media server for a few years, then I switched to using our 2012 Mac mini w/dual 1T PNY SATA SSDs & 16GB of RAM.

Back in those days, I used PNY 2.5" SATA SSD's to upgrade more than a dozen 2010~2012 Mac mini's for self, friends and family. Eventually I ended up getting most of those obsolete Mac mini's back. It was kind of sad pulling those PNY SSDs and putting them into $10 Sabrent 3.0 enclosures. The most amazing part of the story is, that 10 out of 10 of those PNY SSDs and Sabrent enclosures are still in service as Media and Clone backups.

I agree with MartinR that the internal battery should have lasted longer.

The problem is, that might be true if it was just sitting there without anything else connected to it.

In your case, it sounds like other devices including the un-powered main, may have cause the internal battery to drain faster than normal.

My AppleCare expired about nine months ago. According to the support website, I have two options: either a paid repair or phone support. I'm currently exploring whether I can access phone support without a fee. If not, I will just live with it.

Thank you to everyone who shared their experiences and insights on this issue, I really appreciate it.