Findings on macOS Golden Gate: SMC key deprecation (CH0B/CH0C) and transition to PowerUI

[alphastar-avi]

Hi,

While testing the tool on macOS Golden Gate, I noticed battery maintain and manual charging controls stopped functioning because of low-level changes Apple made to the SMC interface.

I investigated how the new OS manages battery limits and wanted to share the findings here in case it helps with updating the backend.

What Fails Currently

1. smc -k CH0B -r returns CH0B [ ] no data. The legacy register keys (CH0B, CH0C, CH0I) are no longer populated.
2. The active charging register is now CHIB ([ui8]). However, writing to it (smc -k CHIB -w 01) fails with:

   Error: SMCWriteKey() = e00002c1 (kIOReturnNotPrivileged)
   

   macOS now enforces SIP entitlements (com.apple.private.applesmc.user-client-access) on AppleSMCClient. Even running as root via sudo is blocked by the kernel.

How macOS Golden Gate Handles Charging Limits Natively

Apple moved charge limiting into powerd and PowerUI.framework (Manual Charge Limit / MCL) via XPC (com.apple.powerui.smartChargeManager).

This interface is accessible in userspace without sudo or SIP disablement through PowerUISmartChargeClient:

Class clientClass = objc_getClass("PowerUISmartChargeClient");
id client = [[clientClass alloc] initWithClientName:@"battery-cli"];

// Enable limit (native supported values: 80, 85, 90, 95, 100)
[client enableMCL:&err];
[client setMCLLimit:80 error:&err];

// Disable limit (restores 100% charging)
[client disableMCL:&err];

When set, powerd registers a ChargeCtrlPolicy in /Library/Preferences/com.apple.powerd.charging.plist with:

• reason: manualChargeLimit
• soclimit: 80
• drain: true
• isEndOfCharge: true

The PMU then cuts charging current to 0 mA and runs the laptop on adapter passthrough.

Note on Periodic Calibration (ChargingUpForGauging)

During testing with this interface, macOS may occasionally charge to 100% before holding at 80%, logging:

SOC limit policy suspend due to mitigation active:1
ChargingUpForGauging (mode: 0)

This is Apple's periodic gas gauge calibration cycle. Once the battery reaches 100% and finishes balancing, powerd clears the mitigation flag and drops back to 80% automatically.

Conclusion

If the project plans to support macOS Golden Gate, adding a fallback path that calls PowerUISmartChargeClient when CH0B returns no data or when SMC writes fail with e00002c1 looks like the cleanest native solution.