[!TIP] Feb 17, 2026 UPDATE: Finally, after more than 5 years, macOS 26.4 and later supports charge limiting natively (adjustable from 80% to 100%), so batt is not needed if the built-in range meets your needs. batt remains useful on older releases and when you want a limit below 80%. On macOS 27-era firmware, batt programs the firmware's charge-limit facility directly.

Note: Use table of contents of quickly navigate to the section you want, e.g., Installation. 👆↗

batt

batt is a tool to control battery charging on Apple Silicon MacBooks.

Why do you need this?

This article might be helpful. TL;DR: keep your battery at 80% or lower when plugged in, and discharge it as shallowly as feasible.

Previously, before optimized battery charging is introduced, MacBooks are known to suffer from battery swelling when they are kept at 100% all the time, especially the 2015s. Even with optimized battery charging, the effect is not optimal (described below).

batt can effectively alleviate this problem by limiting the battery charge level. It can be used to set a maximum charge level. For example, you can set it to 80%, and it will stop charging when the battery reaches 80%.

On older firmware, the computer then runs from wall power and the battery percentage remains steady. On macOS 27-era firmware, Apple changed the mechanism: the firmware may run the Mac from the battery when it is above the limit, so the percentage can drop until it returns to the configured range.

Quick link to installation guide.

Features

batt tried to keep as simple as possible. Charging limiting is the only thing to care about for most users:

• Limit battery charge, with a lower and upper bound, like ThinkPads. Docs

However, if you are nerdy and want to dive into the details, it does have some advanced features for power users. These are shown only when the current Mac's SMC keys support them.

• Control MagSafe LED (if present) according to charge status. Docs
• Cut power from the wall (even if the adapter is physically plugged in) to use battery power. Docs
• On firmware < 20xxx, it solves common sleep-related issues when controlling charging. Docs1 Docs2
• Calibrate battery automatically. Docs

How is it different from XXX?

It is free and opensource. It even comes with some features (like idle sleep preventions and pre-sleep stop charging) that are only available in paid counterparts. It comes with no ads, no tracking, no telemetry, no analytics, no bullshit. It is open source, so you can read the code and verify that it does what it says it does.

It is simple but well-thought. It only does charge limiting and does it well. On firmware < 20xxx, batt handles sleep edge cases that can otherwise let a MacBook charge to 100%. On newer firmware, it delegates the range to Apple SMC so enforcement continues during sleep. Other features are intentionally limited to keep it simple. If you encounter a problem or want an additional feature, please raise an issue.

It is light-weight. No electron GUIs hogging your system resources like some other tools. You can use batt on the command-line, or use the native macOS menubar app if you prefer a GUI. The GUI is written using native macOS APIs, so it is light-weight and fast.

But macOS have similar features built-in, is it?

Yes, macOS have optimized battery charging. It will try to find out your charging and working schedule and prohibits charging above 80% for a couple of hours overnight. However, if you have an un-regular schedule, this will simply not work. Also, you lose predictability (which I value a lot) about your computer's behavior, i.e., by letting macOS decide for you, you, the one who knows your schedule the best, cannot control when to charge or when not to charge.

batt can make sure your computer does exactly what you want. You can set a maximum charge level, and it will stop charging when the battery reaches that level. Therefore, it is recommended to disable macOS's optimized charging when using batt.

Compatibility Matrix

Check your firmware version by running system_profiler SPHardwareDataType | grep -i firmware in Terminal. Do NOT rely on macOS version.

Firmware Version	First macOS release	GUI	CLI (Prebuilt)	CLI (Build from Source)	Note
6723.x.x	macOS 11 Big Sur	❌	❌	⚠️
7429.x.x / 7459.x.x	macOS 12 Monterey	❌	⚠️	✅
8419.x.x / 8422.x.x	macOS 13 Ventura	⚠️	⚠️	✅
101xx.x.x	macOS 14 Sonoma	⚠️	⚠️	✅
118xx.x.x	macOS 15 Sequoia	✅	✅	✅
138xx.x.x / 18xxx.x.x	macOS 26 Tahoe	✅	✅	✅
20xxx.x.x	macOS 27 Golden Gate	✅	✅	✅	Firmware-managed limits; see below
Other	Unknown	❓	❓	❓

• ❌: Unsupported
• ✅: Supported
• ⚠️: Not verified, but expected to work.
• ❓: Unknown, please raise an issue if you have tested it.

[!NOTE] Firmware version is different from macOS version. Old macOS versions may have newer firmware, e.g. macOS 15 with firmware 138xx.x.x (macOS Tahoe version).

batt does not branch on the reported macOS or firmware version. It probes usable SMC keys at runtime (mainly tied to the firmware version, not the macOS version). This also handles an older macOS installation receiving newer firmware.

If you want to know which MacBooks I personally developed it on, I am using it on all my personal MacBooks every single day, including MacBook Air M1 2020 (A2337), MacBook Air M2 2022 (A2681), MacBook Pro 14' M1 Pro 2021 (A2442), MacBook Pro 16' M1 Max 2021 (A2485).

If you encounter any incompatibility, please raise an issue with your MacBook model, firmware version, batt version, macOS version, and batt logs (/tmp/batt.log).

macOS 27 / 20xxx firmware behavior

On firmware exposing bfF0, batt writes the upper and lower percentages to bfD0 and bfE0, activates the limit, and periodically verifies that all three values are still correct. Apple firmware then decides when charging starts and stops. The limit continues to work while macOS and the batt daemon are asleep, so batt does not register sleep notifications or run pre-sleep/post-wake charging hooks in this mode.

This mode has several intentional differences and current limitations:

• If the battery is above the upper limit, firmware can stop drawing wall power and use the battery to run the Mac. Unlike legacy control, the percentage may therefore fall.
• MagSafe LED control is unavailable because batt no longer owns or reliably knows the charging-enabled state.
• Legacy sleep options are unavailable and unnecessary. Incompatible values left in the configuration after an upgrade are disabled by the daemon.

The daemon reports these capabilities to current CLI and GUI clients. Older daemons that do not provide detailed compatibility data retain the previous permissive client behavior.

Installation (GUI Version)

GUI version is a native macOS menubar app. It's not as feature-complete as the command-line version, but it is a good choice if you are not comfortable with the command-line. The command-line version is also included if you have the GUI version.

1. Download .dmg file from Releases and open it (right-click open if macOS says it's damaged)
2. Drag batt.app to Applications
3. macOS may say it's damaged when you try to run it (it's NOT) and wants you to move it to trash. To fix it, run this in Terminal: sudo xattr -r -d com.apple.quarantine /Applications/batt.app.
4. Run batt.app.
5. Follow the MenuBar UI to install or upgrade.
6. It is highly recommended to disable macOS's optimized charging when using batt. To do so, open System Settings -> Battery -> Battery Health -> i -> Turn OFF Optimized Battery Charging. Built-in charge limit also need to be disabled if you are on macOS 26.4 or later.

[!TIP] There are 3rd-party GUI versions built around batt by some amazing opensource developers:

1. BattGUI by @clzoc
2. batt-helper by @zxw5775

Installation (Command-Line Version)

[!NOTE] Command-Line version is already included if you have installed the GUI version. You can run batt in Terminal to use it.

You have two choices to install the CLI version of batt:

1. Homebrew Docs
2. Installation Script (Recommended) Docs

You can choose either one. Please do not use both at the same time to avoid conflicts.

Homebrew

[!IMPORTANT] If you previously ran batt v0.7.3 or earlier with sudo brew services, follow the one-time service-label migration before starting the service. When the Homebrew formula moved from v0.7.3 to v0.7.5, its service label changed from cc.chlc.batt to homebrew.mxcl.batt.

1. brew install batt
2. sudo brew services start batt
3. Please read Notes.

Thank you, @Jerry1144, for bootstrapping the Homebrew formula.

Installation Script

1. (Optional) There is an installation script to help you quickly install batt (Internet connection required). Put this in your terminal: bash <(curl -fsSL https://github.com/charlie0129/batt/raw/master/hack/install.sh). You may need to provide your login password (to control charging). This will download and install the latest stable version for you. Follow the on-screen instructions, then you can skip to step 5.

Manual installation steps

1. Get the binary. For stable and beta releases, you can find the download link in the release page. If you want development versions with the latest features and bug fixes, you can download prebuilt binaries from GitHub Actions (has a retention period of 3 months and you need to chmod +x batt after extracting the archive) or build it yourself .

2. Put the binary somewhere safe. You don't want to move it after installation :). It is recommended to save it in your $PATH, e.g., /usr/local/bin, so you can directly call batt on the command-line. In this case, the binary location will be /usr/local/bin/batt.

3. Install daemon using sudo batt install. If you do not want to use sudo every time after installation, add the --allow-non-root-access flag: sudo batt install --allow-non-root-access. To uninstall: please refer to How to uninstall?

In case you have GateKeeper turned on, you will see something like "batt is can't be opened because it was not downloaded from the App Store" or "batt cannot be opened because the developer cannot be verified". If you don't see it, you can skip this step. To solve this, you can either 1. (recommended) Go to System Settings -> Privacy & Security --scroll-down--> Security -> Open Anyway; or 2. run sudo spctl --master-disable to disable GateKeeper entirely.

Notes

• Test if it works by running sudo batt status. If you see your battery status, you are good to go!
• Time to customize. By default batt will set a charge limit to 60%. For example, to set the charge limit to 80%, run sudo batt limit 80.
• As said before, it is highly recommended to disable macOS's optimized charging when using batt. To do so, open System Settings -> Battery -> Battery Health -> i -> Turn OFF Optimized Battery Charging. Built-in charge limit also need to be disabled if you are on macOS 26.4 or later.
• If your current charge is above the limit, behavior depends on the detected backend. Firmwares < 20xxx stops charging and keeps running from the wall, so the percentage stays steady. 20xxx firmware may run from the battery until it falls back into the configured range.
• You can refer to Usage for additional configurations. Don't know what a command does? Run batt help to see all available commands. To see help for a specific command, run batt help <command>.
• To disable the charge limit, run batt disable or batt limit 100.
• How to uninstall? How to upgrade?

Finally, if you find batt helpful, stars ⭐️ are much appreciated!

Usage

Limit battery charge

Make sure your computer doesn't charge beyond what you said.

Setting the limit to 10-99 will enable the battery charge limit, limiting the maximum charge to somewhere around your setting. However, setting the limit to 100 will disable the battery charge limit.

By default, batt will set a 60% charge limit.

To customize charge limit, see batt limit. For example,to set the limit to 80%, run batt limit 80. To disable the limit, run batt disable or batt limit 100.

To disable the limit only temporarily, use batt disable --for=1d. Your current limit is restored automatically once the duration has elapsed, even if your Mac reboots in the meantime. Durations accept minutes, hours, days and weeks, e.g. 30m, 2h, 1d, 1w. Setting a limit with batt limit before the duration elapses cancels the scheduled restore. batt status shows when the limit will be restored.

Enable/disable power adapter

[!NOTE] This feature is CLI-only and is not available in the GUI version.

Cut or restore power from the wall. This has the same effect as unplugging/plugging the power adapter, even if the adapter is physically plugged in.

This is useful when you want to use your battery to lower the battery charge, but you don't want to unplug the power adapter.

NOTE: if you are using Clamshell mode (using a Mac laptop with an external monitor and the lid closed), cutting power will cause your Mac to go to sleep. This is a limitation of macOS. There are ways to prevent this, but it is not recommended for most users.

To enable/disable power adapter, see batt adapter. For example, to disable the power adapter, run sudo batt adapter disable. To enable the power adapter, run sudo batt adapter enable.

Check status

[!NOTE] This feature is CLI-only and is not available in the GUI version.

Check the current config, battery info, and charging status.

To do so, run sudo batt status. Example output:

Charging status:
  Allow charging: ✘ (refreshes can take up to 2 minutes)
    Your Mac will not charge, because your current charge is above the limit.
  Use power adapter: ✔

Battery status:
  Current charge: 65%
  State: not charging
  Full capacity: 8648 mAh / 8694 mAh (99%)
  Charge rate: +0.0 W
  Voltage: 11.89 V

Battery configuration:
  Upper limit: 60%
  Lower limit: 58%
  Prevent idle-sleep when charging: ✔
  Disable charging before sleep if charge limit is enabled: ✔
  Prevent system-sleep when charging: ✘
  Allow non-root users to access the daemon: ✔
  Control MagSafe LED: ✔

Hardware compatibility:
  Charge control mode: legacy
  Sleep hooks: ✔
  MagSafe LED control: ✔
  Power adapter control: ✔
  Auto calibration: ✔

Calibration status:
  Phase: Idle
  Schedule: disabled

Advanced

These advanced features are not for most users. Using the default setting for these options should work the best.

Auto Calibration (experimental)

Thanks @brookqin for implementing the initial version of this feature.

Automatically performs a full charging cycle to help calibrate reported battery percentage.

Phases: Idle → DischargeToThreshold → ChargeToFull → HoldAfterFull → DischargeAfterHold → RestoreAndFinish → Idle.

Flow:

1. Discharge below configured threshold (defaults to 15%). Charging is forced off.
2. Charge to 100%. Upper limit temporarily set to 100.
3. Hold at 100% for the configured duration (defaults to 120 minutes unless changed).
4. After hold, charging is disabled again and the battery is allowed to naturally discharge back down to the original upper limit snapshot.
5. Restore original upper/lower limits and adapter/charging states and return to Idle.

batt prevents idle system sleep for the entire calibration session, including while paused, and releases the assertion on completion, cancellation, or error. macOS can still force sleep when you close the lid or explicitly choose Sleep, so keep the lid open during calibration.

You can start, pause, resume, cancel via the GUI (Advanced → Auto Calibration) or CLI (batt calibration start|pause|resume|cancel|status) or HTTP API. Cancel restores original settings immediately.

To change the discharge threshold (defaults to 15%), run batt calibration discharge-threshold <percentage>. To change the hold duration (defaults to 120 minutes), run batt calibration hold-duration <minutes>.

Scheduling automatic calibration

[!NOTE] This feature is CLI-only and is not available in the GUI version.

Use batt schedule to let the daemon trigger calibration runs on a cron cadence. Examples:

batt schedule '0 10 * * 0'   # every Sunday at 10:00 (quote * so the shell doesn't expand it)
batt schedule '0 10 1 * *'   # At 10:00 on the first day of every month
batt schedule '0 10 1 */2 *' # At 10:00 on the first day of every two months
batt schedule disable        # remove the schedule and stop future runs
batt schedule postpone 90m   # push the next run back by 90 minutes (defaults to 1h if omitted)
batt schedule skip           # skip only the upcoming run and keep the schedule

After setting a cron expression, the CLI prints the next few run times returned by the daemon so you can verify the schedule. postpone and skip operate on the next scheduled execution only; disable clears the stored cron configuration.

Before a scheduled calibration actually begins, batt checks that the Mac is plugged into wall power. If it is not, the scheduler posts a reminder notification (GUI) and keeps waiting for roughly five minutes. If power is still unavailable after that grace period, the pending run is skipped automatically so later schedules are not blocked.

Preventing idle sleep

[!NOTE] This is a legacy-control option for older firmware < 20xxx. It is unavailable and unnecessary with 20xxx firmware, where the firmware enforces limits during sleep.

Set whether to prevent idle sleep during a charging session.

Due to macOS limitations, batt will be paused when your computer goes to sleep. As a result, when you are in a charging session and your computer goes to sleep, there is no way for batt to stop charging (since batt is paused by macOS) and the battery will charge to 100%. This option, together with disable-charging-pre-sleep, will prevent this from happening.

This option tells macOS NOT to go to sleep when the computer is in a charging session, so batt can continue to work until charging is finished. Note that it will only prevent idle sleep, when 1) charging is active 2) battery charge limit is enabled. So your computer can go to sleep as soon as a charging session is completed.

However, this options does not prevent manual sleep (limitation of macOS). For example, if you manually put your computer to sleep (by choosing the Sleep option in the top-left Apple menu) or close the lid, batt will still be paused and the issue mentioned above will still happen. This is where disable-charging-pre-sleep comes in. See Disabling charging before sleep.

To enable this feature, run sudo batt prevent-idle-sleep enable. To disable, run sudo batt prevent-idle-sleep disable.

Disabling charging before sleep

[!NOTE] This is a legacy-control option for older firmware < 20xxx. It is unavailable and unnecessary with 20xxx firmware, where the firmware enforces limits during sleep.

Set whether to disable charging before sleep if charge limit is enabled.

As described in Preventing idle sleep, batt will be paused by macOS when your computer goes to sleep, and there is no way for batt to continue controlling battery charging. This option will disable charging just before sleep, so your computer will not overcharge during sleep, even if the battery charge is below the limit.

To enable this feature, run sudo batt disable-charging-pre-sleep enable. To disable, run sudo batt disable-charging-pre-sleep disable.

Prevent system sleep

[!NOTE] This is a legacy-control option for older firmware < 20xxx. It is unavailable with 20xxx firmware.

Set whether to prevent system sleep during a charging session (experimental).

This option tells macOS to create power assertion, which prevents sleep, when all conditions are met:

1. charging is active
2. battery charge limit is enabled
3. computer is connected to charger.

So your computer can go to sleep as soon as a charging session is completed / charger disconnected.

Does similar thing to Preventing idle sleep, but works for manual sleep too.

Note: Please disable Preventing idle sleep and Disabling charging before sleep, while this feature is in use.

To enable this feature, run sudo batt prevent-system-sleep enable. To disable, run sudo batt prevent-system-sleep disable.

Upper and lower charge limit

[!NOTE] This feature is CLI-only and is not available in the GUI version.

When you set a charge limit, for example, on a Lenovo ThinkPad, you can set two percentages. The first one is the upper limit, and the second one is the lower limit. When the battery charge is above the upper limit, the computer will stop charging. When the battery charge is below the lower limit, the computer will start charging. If the battery charge is between the two limits, the computer will keep whatever charging state it is in.

batt have similar features built-in. The charge limit you have set (using batt limit) will be used as the upper limit. By default, The lower limit will be set to 2% less than the upper limit. To customize the lower limit, use batt lower-limit-delta.

For example, if you want to set the lower limit to be 5% less than the upper limit, run sudo batt lower-limit-delta 5. So, if you have your charge (upper) limit set to 60%, the lower limit will be 55%.

Control MagSafe LED

Acknowledgement: @exidler

This option makes the MagSafe LED reflect the charging state of your MacBook (or force it off).

• Green: charge limit is reached and charging is stopped.
• Orange: charging is in progress.
• Off: just woken up from sleep, charing is disabled and batt is waiting before controlling charging.

Note that you must have a MagSafe LED on your MacBook to use this feature.

This also requires legacy direct charging control. It is unavailable on macOS 27 / 20xxx firmware even if the Mac has a physical MagSafe LED, because firmware owns the charging decision and batt cannot reliably mirror its state.

To enable MagSafe LED control, run sudo batt magsafe-led enable.

To force the MagSafe LED to stay off, run sudo batt magsafe-led always-off.

Check logs

Logs are directed to /tmp/batt.log. If something goes wrong, you can check the logs to see what happened. Raise an issue with the logs attached.

Building

You need to install command line developer tools (by running xcode-select --install) and Go (follow the official instructions here).

CLI

make

Simply running make in this repo should build the binary into ./bin/batt. You can then follow the upgrade guide to install it (you just use the binary you have built, not downloading a new one, of course).

GUI

make app

This will build the GUI version of batt into ./bin/batt.app. Drag it to /Applications and run it.

Architecture

You can think of batt like docker. It has a daemon that runs in the background, and a client (CLI or GUI) that communicates with the daemon. They communicate through unix domain socket as a way of IPC. The daemon does the actual heavy-lifting, and is responsible for controlling battery charging. The client is responsible for sending users' requirements to the daemon.

For example, when you run sudo batt limit 80, the client will send the requirement to the daemon, and the daemon will do its job to keep the charge limit to 80%.

The daemon selects one of two control backends from SMC key presence. The legacy backend continuously reads battery percentage and toggles charging itself. The firmware backend writes lower/upper limits and periodically reconciles them while Apple firmware enforces the range, including during sleep. The same capability data is exposed to CLI and GUI clients so unsupported features are not offered.

Motivation

I created this tool simply because I am not satisfied with existing tools 😐.

I have written and using similar utils (to limit charging) on Intel MacBooks for years. Finally I got hands on an Apple Silicon MacBook (yes, 2 years later since it is introduced 😅 and I just got my first one). The old BCLM way to limit charging doesn't work anymore. I was looking for a tool to limit charging on M1 MacBooks.

I have tried some alternatives, both closed source and open source, but I kept none of them. Some paid alternatives' licensing options are just too limited 🤔, a bit bloated, require periodic Internet connection (hmm?) and are closed source. It doesn't seem a good option for me. Some open source alternatives just don't handle edge cases well and I encountered issues regularly especially when sleeping (as of Apr 2023).

I want a simple tool that does just one thing, and does it well -- limiting charging, just like the Unix philosophy. It seems I don't have any options but to develop by myself. So I spent a weekend developing an MVP, so here we are! batt is here!

FAQ

How to uninstall?

GUI version

Click Uninstall Daemon... to uninstall. After the daemon is uninstalled, you can remove the batt.app from your Applications folder.

CLI version

Note that you should choose the same method as you used to install batt to uninstall it.

If you don't remember how you installed it, you can check the binary location by running which batt. If it is in /usr/local/bin, you probably used the installation script. If it is in /opt/homebrew/bin, you probably used Homebrew.

Script-installed:

1. Run sudo batt uninstall to remove the daemon.
2. Remove the config by sudo rm -f /etc/batt*.
3. Remove the batt binary itself by sudo rm $(which batt).

Homebrew-installed:

1. Run sudo batt disable to restore the default charge limit.
2. Run sudo brew services stop batt to stop the daemon.
3. Run brew uninstall batt to uninstall the binary.
4. Remove the config by sudo rm -f /opt/homebrew/etc/batt.json && sudo rm -f /etc/batt*.

How to upgrade?

GUI version

Just follow the installation steps again. After you open the new version of batt.app, click Upgrade Daemon... upgrade to the new daemon.

CLI version

Note that you should choose the same method as you used to install batt to upgrade it.

If you don't remember how you installed it, you can check the binary location by running which batt. If it is in /usr/local/bin, you probably used the installation script. If it is in /opt/homebrew/bin, you probably used Homebrew.

Script-installed:

bash <(curl -fsSL https://github.com/charlie0129/batt/raw/master/hack/install.sh)

Homebrew-installed:

Homebrew service-label migration

If you previously ran batt v0.7.3 or earlier with sudo brew services, use the following commands once. When the Homebrew formula moved from v0.7.3 to v0.7.5, its service label changed from cc.chlc.batt to homebrew.mxcl.batt, and brew services stop batt may not stop the job registered under the old label. The old job must be booted out before its plist is removed; deleting the plist alone does not unregister a running job from launchd.

sudo brew services stop batt
if sudo launchctl print system/cc.chlc.batt >/dev/null 2>&1; then
  sudo launchctl bootout system/cc.chlc.batt
fi
sudo rm -f /Library/LaunchDaemons/cc.chlc.batt.plist
brew upgrade batt
sudo brew services start batt

No uninstall or reinstall is needed. For later Homebrew upgrades, use the normal procedure:

sudo brew services stop batt
brew upgrade batt
sudo brew services start batt

Manual:

1. Run sudo batt uninstall to remove the old daemon.
2. Download the new binary. For stable and beta releases, you can find the download link in the release page. If you want development versions with the latest features and bug fixes, you can download prebuilt binaries from GitHub Actions (has a retention period of 3 months and you need to chmod +x batt after extracting the archive) or build it yourself .
3. Replace the old batt binary with the downloaded new one. sudo cp ./batt $(where batt)
4. Run sudo batt install to install the daemon again. Although most config is preserved, some security related config is intentionally reset during re-installation. For example, if you used --allow-non-root-access when installing previously, you will need to use it again like this sudo batt install --allow-non-root-access.

Why is it Apple Silicon only?

You probably don't need this on Intel :p

On Intel MacBooks, you can control battery charging in a much, much easier way, simply setting the BCLM key in Apple SMC to the limit you need, and you are all done. There are many tools available. For example, you can use smc-command to set SMC keys. Of course, you will lose some advanced features like upper and lower limit.

However, on Apple Silicon, the way how charging is controlled changed. There is no such key. Therefore, we have to use a much more complicated way to achieve the same goal, and handle more edge cases, hence batt.

Will there be an Intel version?

Probably not. batt was made Apple-Silicon-only after some early development. I have tested batt on Intel during development (you can probably find some traces from the code :). Even though some features in batt are known to work on Intel, some are not. Development and testing on Intel requires additional effort, especially those feature that are not working. Considering the fact that Intel MacBooks are going to be obsolete in a few years and some similar tools already exist (without some advanced features), I don't think it is worth the effort.

Why does my MacBook stop charging after I close the lid?

[!NOTE] This FAQ applies only to older firmware < 20xxx using direct charging control. On 20xxx firmware, the charge limit persists through sleep and batt does not disable charging before sleep.

TL,DR; This is intended, and is the default behavior. It is described here. You can turn this feature off by running sudo batt disable-charging-pre-sleep disable (not recommended, keep reading).

But it is suggested to keep the default behavior to make your charge limit work as intended. Why? Because when you close the lid, your MacBook will go into forced sleep, and batt will be paused by macOS. As a result, batt can no longer control battery charging. It will be whatever state it was before you close the lid. This is the problem. Let's say, if you close the lid when your MacBook is charging, since batt is paused by macOS, it will keep charging, ignoring the charge limit you have set. There is no way to prevent forced sleep. Therefore, the only way to solve this problem is to disable charging before sleep. This is what batt does. It will disable charging just before your MacBook goes to sleep, and re-enable it when it wakes up. This way, your Mac will not overcharge during sleep.

Not that you will encounter this forced sleep only if you, the user, forced the Mac to sleep, either by closing the lid or selecting the Sleep option in the Apple menu. If your Mac decide to sleep by itself, called idle sleep, i.e. when it is idle for a while, in this case, you will not experience this stop-charging-before-sleep situation.

So it is suggested to keep this feature on. But What if I MUST let my Mac charge during a forced sleep without turing off disable-charging-pre-sleep, even if it may charge beyond the charge limit? This is simple, just disable charge limit batt disable. This way, when you DO want to enable charge limit again, disable-charging-pre-sleep will still be there to prevent overcharging. The rationale is: when you want to charge during a forced sleep, you actually want heavy use of your battery and don't want ANY charge limit at all, e.g. when you are on a long outside-event, and you want to charge your Mac when it is sitting in your bag, lid closed. Setting the charge limit to 100% is equivalent to disabling charge limit. Therefore, most batt features will be turned off and your Mac can charge as if batt is not installed.

Why does it require root privilege?

It writes to SMC to control battery charging. This does changes to your hardware, and is a highly privileged operation. Therefore, it requires root privilege.

If you are concerned about security, you can check the source code here to make sure it does not do anything funny.

Why is it written in Go and C?

Since it is a hobby project, I want to balance effort and the final outcome. Go seems a good choice for me. However, C is required to register sleep and wake notifications using Apple's IOKit framework. Also, Go don't have any library to r/w SMC, so I have to write it myself (charlie0129/gosmc). This part is also mainly written in C as it interacts with the hardware and uses OS capabilities. Thankfully, writing a library didn't slow down development too much.

Why is there so many logs?

By default, batt daemon will have its log level set to debug for easy debugging. The debug logs are helpful when reporting problems since it contains useful information. So it is recommended to keep it as debug. You may find a lot of logs in /tmp/batt.log after you use your Mac for a few days. However, there is no need to worry about this. The logs will be cleaned by macOS on reboot. It will not grow indefinitely.

If you believe you will not encounter any problem in the future and still want to set a higher log level, you can achieve this by:

1. Stop batt: sudo launchctl unload /Library/LaunchDaemons/cc.chlc.batt.plist (batt must be stopped to change config so you can't skip this step)
2. Use your preferred editor to edit /Library/LaunchDaemons/cc.chlc.batt.plist and change the value of -l=debug to your preferred level. The default value is debug.
3. Start batt again: sudo launchctl load /Library/LaunchDaemons/cc.chlc.batt.plist

Why does my Mac go to sleep when I disable the power adapter?

You are probably using Clamshell mode, i.e., using a Mac laptop with an external monitor and the lid closed. This is a limitation of macOS. Clamshell mode MUST have power connected, otherwise, the Mac will go to sleep.

If you want to prevent this, you need to disable sleep globally using pmset, or you can use a third-party app like Amphetamine to prevent sleep.

My Mac does not start charging after waking up from sleep

[!NOTE] This FAQ applies only to older firmware < 20xxx using legacy direct charging control. 20xxx firmware has no batt post-wake delay.

This is expected. batt will prevent your Mac from charging temporarily if your Mac has just woken up from sleep. This is to prevent overcharging during sleep. Your Mac will start charging soon (at most 2 minutes).

If you absolutely need to charge your Mac immediately after waking up from sleep, you can disable this feature by running sudo batt disable-charging-pre-sleep disable. However, this is not recommended (see Disabling charging before sleep).

Why does my Mac starts charging after entering sleep?

[!NOTE] This FAQ applies only to older firmware < 20xxx using legacy direct charging control. 20xxx firmware continues enforcing the configured range during sleep.

If you are using the default batt settings (i.e., prevent-idle-sleep and disable-charging-pre-sleep are both enabled), this should not happen.

However, there are some cases like #101 where hibernation mode is unexpectedly changed by the user. Your Mac may enter hibernation immediately instead of sleep, and Mac firmware resets SMC keys after hibernation, causing batt to lose control of charging.

To see if you are in always-hibernate mode, run pmset -g | grep hibernatemode. If the value is not 0 nor 3, you are in always-hibernate mode. To change it back to sleep mode, run sudo pmset -a hibernatemode 3 (factory default for MacBooks, hibernates after several hours) or sudo pmset -a hibernatemode 0 (never hibernate). After changing the mode, reboot your Mac for the change to take effect.

Can I quit the GUI app?

Yes.

As in #62, you can quit the GUI app and expect batt to continue working, provided that you have installed the daemon during the first run.

You may also want to remove the GUI app from System Settings -> General -> Login Items & Extensions to prevent it from starting automatically on login. Important: only remove the GUI app from Open at Login, do NOT remove the daemon from Allow in Background.

The reason behind is that the GUI app does not do the actual battery charge controlling. The daemon does. As long as the daemon is not uninstalled, charging control will work. The GUI app is just a client to communicate with the daemon. Quitting the GUI app will not affect the daemon. You can save some menu bar space if you rarely change settings.

Will batt work after shutdown?

No. batt only works when macOS is running. After shutdown, there is no way to control battery charging until macOS boots up again.

Acknowledgements

• actuallymentor/battery for various SMC keys.
• hholtmann/smcFanControl for its C code to read/write SMC, which inspires charlie0129/gosmc.
• Apple for its guide to register and unregister sleep and wake notifications.
• @exidler for building the MagSafe LED controlling logic.
• @pichxyaponn for the initial version of GUI.
• @MabaKalox for prevent-system-sleep feature.
• @peterneutron for refactoring the power metrics code and the power flow feature.
• @invisiblepixel for app icon design.
• @brookqin for implementing auto calibration.
• @ashwinr64 for investigating SMC keys on macOS 27 #140 comment actuallymentor/battery#469, also @lilianmoraru for the initial PR.

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