本文轉載自:https://blog.csdn.net/wateryi/article/details/50834821

在android系統中，電池資訊是由BatteryService.java統一管理的，在BatteryService中，通過：

IBinder b = ServiceManager.getService("batteryproperties");
final IBatteryPropertiesRegistrar batteryPropertiesRegistrar =
        IBatteryPropertiesRegistrar.Stub.asInterface(b);
try {
    batteryPropertiesRegistrar.registerListener(new BatteryListener());
} catch (RemoteException e) {
    // Should never happen.
}
    向註冊回撥函式，電池資訊一旦有更新，就會呼叫BatteryListener中的batteryPropertiesChanged介面：
private final class BatteryListener extends IBatteryPropertiesListener.Stub {
    @Override
    public void batteryPropertiesChanged(BatteryProperties props) {
        final long identity = Binder.clearCallingIdentity();
        try {
            BatteryService.this.update(props);
        } finally {
            Binder.restoreCallingIdentity(identity);
        }
   }
}
    進而呼叫update函式更新電池資訊類：BatteryProperties; 而通常上層接收的電池資訊廣播也是通過BatteryService中的sendIntentLocked傳送的：
private void sendIntentLocked() {
    //  Pack up the values and broadcast them to everyone
    final Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
    intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
            | Intent.FLAG_RECEIVER_REPLACE_PENDING);
 
    int icon = getIconLocked(mBatteryProps.batteryLevel);
 
    intent.putExtra(BatteryManager.EXTRA_STATUS, mBatteryProps.batteryStatus);
intent.putExtra(BatteryManager.EXTRA_STATUS_SMARTBOOK, mBatteryProps.batteryStatus_smb);
    intent.putExtra(BatteryManager.EXTRA_HEALTH, mBatteryProps.batteryHealth);
    intent.putExtra(BatteryManager.EXTRA_PRESENT, mBatteryProps.batteryPresent);
intent.putExtra(BatteryManager.EXTRA_PRESENT_SMARTBOOK, mBatteryProps.batteryPresent_smb);
    intent.putExtra(BatteryManager.EXTRA_LEVEL, mBatteryProps.batteryLevel);
intent.putExtra(BatteryManager.EXTRA_LEVEL_SMARTBOOK, mBatteryProps.batteryLevel_smb);
    intent.putExtra(BatteryManager.EXTRA_SCALE, BATTERY_SCALE);
    intent.putExtra(BatteryManager.EXTRA_ICON_SMALL, icon);
    intent.putExtra(BatteryManager.EXTRA_PLUGGED, mPlugType);
    intent.putExtra(BatteryManager.EXTRA_VOLTAGE, mBatteryProps.batteryVoltage);
    intent.putExtra(BatteryManager.EXTRA_TEMPERATURE, mBatteryProps.batteryTemperature);
    intent.putExtra(BatteryManager.EXTRA_TECHNOLOGY, mBatteryProps.batteryTechnology);
    intent.putExtra(BatteryManager.EXTRA_INVALID_CHARGER, mInvalidCharger);
 
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            ActivityManagerNative.broadcastStickyIntent(intent, null, UserHandle.USER_ALL);
        }
    });
}
    所以我們上層得到電池資訊可以通過廣播獲取：
private BroadcastReceiver mChargeReceiver = new BroadcastReceiver() {
 
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (action.equals(Intent.ACTION_BATTERY_CHANGED)) {
            int status = intent.getIntExtra("status", 0);
            int chargeLevel = intent.getIntExtra("level", 0);
            
            Log.i("wrx_charge", "status = " + status);
            Log.i("wrx_charge", "chargeLevel = " + chargeLevel);
            
            String chargeStatus = "";
            
            switch (status) {
                case BatteryManager.BATTERY_STATUS_UNKNOWN:
                    chargeStatus = mContext.getString(R.string.bird_keyguard_charge_unknow);
                    break;
                case BatteryManager.BATTERY_STATUS_CHARGING:
                    chargeStatus = mContext.getString(R.string.bird_keyguard_charge_charging);
                    break;
                case BatteryManager.BATTERY_STATUS_DISCHARGING:
                    chargeStatus = mContext.getString(R.string.bird_keyguard_charge_discharging);
                    break;
                case BatteryManager.BATTERY_STATUS_NOT_CHARGING:
                    chargeStatus = mContext.getString(R.string.bird_keyguard_charge_notcharging);
                    break;
                case BatteryManager.BATTERY_STATUS_FULL:
                    chargeStatus = mContext.getString(R.string.bird_keyguard_charge_chargefull);
                    break;
            }
            
            mChargeString = chargeLevel + "% " + chargeStatus;
            
            if (status == BatteryManager.BATTERY_STATUS_CHARGING || status == BatteryManager.BATTERY_STATUS_FULL) {
                isCharging = true;
            } else {
                isCharging = false;
            }
            
            onChargeChanged();
        }
    }
};
 
private void registerChargeReceiver() {
    final IntentFilter filter = new IntentFilter();
    filter.addAction(Intent.ACTION_BATTERY_CHANGED);
    getContext().registerReceiver(mChargeReceiver, filter);
}
 
private void unregisterChargeReceiver() {
    getContext().unregisterReceiver(mChargeReceiver);
}
    其實手機內部的linux核心的目錄下也是有相關電池資訊節點的；具體目錄如下：
#define AC_ONLINE_PATH "/sys/class/power_supply/ac/online"
#define USB_ONLINE_PATH "/sys/class/power_supply/usb/online"
#define BATTERY_STATUS_PATH "/sys/class/power_supply/battery/status"
#define BATTERY_HEALTH_PATH "/sys/class/power_supply/battery/health"
#define BATTERY_PRESENT_PATH "/sys/class/power_supply/battery/present"
#define BATTERY_CAPACITY_PATH "/sys/class/power_supply/battery/capacity"
#define BATTERY_VOLTAGE_PATH "/sys/class/power_supply/battery/batt_vol"
#define BATTERY_TEMPERATURE_PATH "/sys/class/power_supply/battery/batt_temp"
#define BATTERY_TECHNOLOGY_PATH "/sys/class/power_supply/battery/technology"
其中capacity的值就是電池電量的值；我們可以通過以下方式去讀取手機相關節點下的值（試過在eng手機中是可以獲取到的，不知道user手機會不會存在相關許可權問題？）：
try {  
    FileReader localFileReader = new FileReader("檔案路徑");  
    BufferedReader localBufferedReader = new BufferedReader(localFileReader, 8192);  
    str2 = localBufferedReader.readLine();//獲取到的檔案中的值
 
    localBufferedReader.close();  
 
} catch (IOException e) {
}