@Override
public void onReceive(Context context, Intent intent) {
int status = intent.getIntExtra(BatteryManager.EXTRA_STATUS,
    BatteryManager.BATTERY_STATUS_UNKNOWN);

    if (status == BatteryManager.BATTERY_STATUS_CHARGING
        || status == BatteryManager.BATTERY_STATUS_FULL)
        Toast.makeText(context, "Charging!", Toast.LENGTH_SHORT).show();
    else
        Toast.makeText(context, "Not Charging!", Toast.LENGTH_SHORT).show();
}

Manifesto:

<receiver android:name=".receiver.BatteryReceiver">
    <intent-filter>
        <action android:name="android.intent.action.ACTION_POWER_CONNECTED"/>
        <action android:name="android.intent.action.ACTION_POWER_DISCONNECTED"/>
        <action android:name="android.intent.action.BATTERY_CHANGED" />
    </intent-filter>
</receiver>

Nesse código, o Toast sempre mostra "Not Charging!". Eu testei isso em um dispositivo real, e quando eu o conecto na alimentação CA ou USB, ele ainda exibe a mensagem "Not Charging!" Torrada.