The feature to disable DeviceOS management of the PMIC has been added in https://github.com/particle-iot/device-os/pull/2015 and is included in 1.5.0-rc.1.
SystemPowerConfiguration conf;
conf.feature(SystemPowerFeature::DISABLE);
System.setPowerConfiguration(conf);
It’s better to run this in STARTUP()
macro, as otherwise in order for this feature flag to take effect, a reset will be required.