What to do when Time Machine incorrectly says your computer is on battery

Automated Time Machine backups should be a “set it and forget it” strategy. Once enabled, macOS warns you only when something goes wrong. No alerts, and–almost always–the backups have continued apace. (macOS automatically runs verification tests on Time Machine volumes, or you can perform one manually.)

A Macworld reader started to receive this message on their laptop Mac and needed help diagnosing it:

No Backups for X Days

The most recent backup did not complete because your computer was running on battery.

This warning improbably appears when their laptop is plugged into power. They tried performing a manual backup and were also told their machine was on battery power, and the backup couldn’t be completed.

This message may be accurate for some users, but it often appears in the wrong circumstances. To add confusion, the alert sometimes occurs after a successful Time Machine backup, baffling users as to why it popped up at all.

Here are a few things to try to stop the alert from appearing, though you may find none work.

Drive issue

If you’re plugging in a drive directly to your laptop or using a networked Time Machine backup, some users have found the battery alert appears when the Time Machine volume has a fault. Run Disk Utility and repair the Time Machine volume.

Because Time Machine maintains an active state on volumes it uses, you may need to disable Time Machine (in System Settings > General > Time Machine) in order to repair a backup volume.

Optimized charging or Low Power Mode active

Optimized charging on Apple laptops tries to extend battery life by monitoring your behavior over time. If patterns develop in which there are long periods–typically overnight–in which your laptop is plugged in, macOS will charge your computer first to 80 percent, then hold it there, and only charge to 100 percent in time for when you typically take your Mac off charging for commuting or daily work.

Keeping a battery at 80 percent of potential charge reduces unnecessary heating, but it may also disrupt Time Machine backups. A laptop can “think” it’s using a battery charge even when plugged in. Disabling optimized power in System Settings > Battery by clicking the info (i) icon to the right of Battery Health. Disable Optimized Battery Charging. The tradeoff is potentially affecting the long-term capacity and lifespan of your battery.

Low Power Mode might also be a culprit. Make sure that you have Low Power Mode set to Never or Only on Battery in the Battery settings panel.

Battery power on networked volume

If you’re backing up your Mac to a drive attached to another Mac on the network, that Mac can’t be on battery power, either–nor can macOS think it is. If the networked destination is a laptop, make sure you test changing the settings above on it, too.

Enable Time Machine backups on battery power

The alert noted above seems to be in line with the Time Machine option in System Settings > General > Time Machine when you click Options: “Back up on battery power.” When this setting is turned off, you would expect that Time Machine backups do not occur when the laptop is not plugged into power.

Conversely, if the setting is on, Time Machine should perform backups even when using battery power. This may eliminate the error and alert this column is about–but not all users have found that changing the setting does.

None of the above may solve the problem

Sadly, even after you’ve made all of the changes above you can’t be sure that the alert will go away or that backups will finish. That’s the case for the correspondent who wrote in with this question. Reports of this problem date to at least macOS 13 Ventura (fall 2022), so it may be a persistent, erratic bug that Apple still needs to quash or provide more guidance to users when it appears.

What you can do whenever you see this alert after going through the troubleshooting in this column is to use the Time Machine menu bar icon to note when the last backup occurred. If you don’t see this icon, go to System Settings > Control Center and, under Menu Bar Only settings, choose Show in Menu Bar for Time Machine. Even then, some backups may still fail, claiming erratically that your laptop is using battery power.

This Mac 911 article is in response to a question submitted by Macworld reader Robert.

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