When android fires ACTION_BATTERY_LOW

Question

In my application, I want to do something when the battery is low. When battery is low android fires ACTION_BATTERY_LOW and when the battery again reaches to its good health it fires intent ACTION_BATTERY_OKAY. So, I have three questions regarding this:

1.At what battery percentage android actually fires ACTION_BATTERY_LOW?

2.Does it fire that same event repeatedly if the battery gets even lower?

3.Can we configure the battery percentage at which android will fire ACTION_BATTERY_LOW intent?

I am more concerned about the third point.

Answer 1

No, you cannot set when the ACTION_BATTERY_LOW threshold will be sent. That is a system level intent that is specified by the Android ROM. Here is the code where it sets the value in the Battery Service:

mLowBatteryWarningLevel = mContext.getResources().getInteger(
            com.android.internal.R.integer.config_lowBatteryWarningLevel);

See the code below which is cut from the Android system code in the update method of the Battery Service:

/* The ACTION_BATTERY_LOW broadcast is sent in these situations:
         * - is just un-plugged (previously was plugged) and battery level is
         *   less than or equal to WARNING, or
         * - is not plugged and battery level falls to WARNING boundary
         *   (becomes <= mLowBatteryWarningLevel).
         */
        final boolean sendBatteryLow = !plugged
            && mBatteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN
            && mBatteryLevel <= mLowBatteryWarningLevel
            && (oldPlugged || mLastBatteryLevel > mLowBatteryWarningLevel);

        sendIntent();

        // Separate broadcast is sent for power connected / not connected
        // since the standard intent will not wake any applications and some
        // applications may want to have smart behavior based on this.
        Intent statusIntent = new Intent();
        statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
        if (mPlugType != 0 && mLastPlugType == 0) {
            statusIntent.setAction(Intent.ACTION_POWER_CONNECTED);
            mContext.sendBroadcast(statusIntent);
        }
        else if (mPlugType == 0 && mLastPlugType != 0) {
            statusIntent.setAction(Intent.ACTION_POWER_DISCONNECTED);
            mContext.sendBroadcast(statusIntent);
        }

        if (sendBatteryLow) {
            mSentLowBatteryBroadcast = true;
            statusIntent.setAction(Intent.ACTION_BATTERY_LOW);
            mContext.sendBroadcast(statusIntent);

Answer 2

That intent is fired from the BatteryService. You'll have to analyze the code a bit, but I'm pretty sure it does not fire repeatedly:

http://gitorious.org/android-eeepc/base/blobs/fda6fae156e31a287e3cfbf66e51ea1405cdf479/services/java/com/android/server/BatteryService.java

The actual values that it fires at are setup in the android resources, so it's configurable only during a system build. This is what we have for our hardware, but this will likely be different for each hardware platform that Android runs on:

<!-- Display low battery warning when battery level dips to this value -->
<integer name="config_lowBatteryWarningLevel">15</integer>

<!-- Close low battery warning when battery level reaches this value -->
<integer name="config_lowBatteryCloseWarningLevel">20</integer>

Unless you're developing a custom hardware platform, I wouldn't make any assumptions about what these values are set to.