1、讲在最前面

系统rom定制开发中，其中在低电量时，系统会自动关机，这个和不同的平台和底层驱动和硬件都有关系，需要结合这些来实际调整这个值，我们可以通过分析源码中电池服务的代码，然后进行修改如何实现这个功能。

2、系统中framework修改低电量关机值的核心类

frameworks\base\services\core\java\com\android\server\BatteryService.java

    private final class HealthHalCallback extends IHealthInfoCallback.Stubimplements HealthServiceWrapper.Callback {@Override public void healthInfoChanged(android.hardware.health.V2_0.HealthInfo props) {BatteryService.this.update(props);}private void update(android.hardware.health.V2_0.HealthInfo info) {traceBegin("HealthInfoUpdate");Trace.traceCounter(Trace.TRACE_TAG_POWER, "BatteryChargeCounter",info.legacy.batteryChargeCounter);Trace.traceCounter(Trace.TRACE_TAG_POWER, "BatteryCurrent",info.legacy.batteryCurrent);synchronized (mLock) {mRealBatteryLevel = info.legacy.batteryLevel;if (!mUpdatesStopped) {mHealthInfo = info.legacy;// Process the new values.processValuesLocked(false);mLock.notifyAll(); // for any waiters on new info} else {copy(mLastHealthInfo, info.legacy);}}traceEnd();}private void processValuesLocked(boolean force) {boolean logOutlier = false;long dischargeDuration = 0;mBatteryLevelCritical =mHealthInfo.batteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN&& mHealthInfo.batteryLevel <= mCriticalBatteryLevel;if (mHealthInfo.chargerAcOnline) {mPlugType = BatteryManager.BATTERY_PLUGGED_AC;} else if (mHealthInfo.chargerUsbOnline) {mPlugType = BatteryManager.BATTERY_PLUGGED_USB;} else if (mHealthInfo.chargerWirelessOnline) {mPlugType = BatteryManager.BATTERY_PLUGGED_WIRELESS;} else {mPlugType = BATTERY_PLUGGED_NONE;}if (DEBUG) {Slog.d(TAG, "Processing new values: "+ "info=" + mHealthInfo+ ", mBatteryLevelCritical=" + mBatteryLevelCritical+ ", mPlugType=" + mPlugType);}// Let the battery stats keep track of the current level.try {mBatteryStats.setBatteryState(mHealthInfo.batteryStatus, mHealthInfo.batteryHealth,mPlugType, mHealthInfo.batteryLevel, mHealthInfo.batteryTemperature,mHealthInfo.batteryVoltage, mHealthInfo.batteryChargeCounter,mHealthInfo.batteryFullCharge);} catch (RemoteException e) {// Should never happen.}...
}private void shutdownIfNoPowerLocked() {// shut down gracefully if our battery is critically low and we are not powered.// wait until the system has booted before attempting to display the shutdown dialog.if (shouldShutdownLocked()) {/*SPRD : add power debug log start*/Slog.d(TAG, "Low battery shutdown, batteryLevel : " + mHealthInfo.batteryLevel);/*SPRD : add power debug log end*/mHandler.post(new Runnable() {@Overridepublic void run() {if (mActivityManagerInternal.isSystemReady()) {Intent intent = new Intent(Intent.ACTION_REQUEST_SHUTDOWN);intent.putExtra(Intent.EXTRA_KEY_CONFIRM, false);intent.putExtra(Intent.EXTRA_REASON,PowerManager.SHUTDOWN_LOW_BATTERY);intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);mContext.startActivityAsUser(intent, UserHandle.CURRENT);}}});}}private boolean shouldShutdownLocked() {if (mHealthInfo.batteryLevel > 0) {return false;}// Battery-less devices should not shutdown.if (!mHealthInfo.batteryPresent) {return false;}// add for bug#1021541boolean checkPlugState = (mUpdatesStopped && mHealthInfo.batteryLevel == mSetBatteryLevel&& mSetBatteryLevel != mRealBatteryLevel);if (DEBUG) Slog.d(TAG, "shutdownIfNoPowerLocked: mUpdatesStopped: " + mUpdatesStopped+ " mHealthInfo.batteryLevel:"  + mHealthInfo.batteryLevel+ " mSetBatteryLevel:" + mSetBatteryLevel + " mRealBatteryLevel:" + mRealBatteryLevel);return !checkPlugState || mHealthInfo.batteryStatus != BatteryManager.BATTERY_STATUS_CHARGING;}private boolean shouldShutdownLocked() {
//add startif (mHealthInfo.batteryLevel <= 2) {return true;}//add endif (mHealthInfo.batteryLevel > 0) {return false;}// Battery-less devices should not shutdown.if (!mHealthInfo.batteryPresent) {return false;}// add for bug#1021541boolean checkPlugState = (mUpdatesStopped && mHealthInfo.batteryLevel == mSetBatteryLevel&& mSetBatteryLevel != mRealBatteryLevel);if (DEBUG) Slog.d(TAG, "shutdownIfNoPowerLocked: mUpdatesStopped: " + mUpdatesStopped+ " mHealthInfo.batteryLevel:"  + mHealthInfo.batteryLevel+ " mSetBatteryLevel:" + mSetBatteryLevel + " mRealBatteryLevel:" + mRealBatteryLevel);return !checkPlugState || mHealthInfo.batteryStatus != BatteryManager.BATTERY_STATUS_CHARGING;}

经过源码分析，如果满足shouldShutdownLocked(),如果满足关机执行 Intent.ACTION_REQUEST_SHUTDOWN
添加

   if (mHealthInfo.batteryLevel <= 2) {return true;}