Some refinements:

- only show the bigtext notification if the device has set extended battery info
- custom icon for the low battery notification (with license information)
- show device name in the notification
- set the notification to high priority
- the battery threshold is now set in GBDevice

LICENSE.artwork

@@ -1,10 +1,13 @@
 The following artwork is licensed under the following licenses
 
 Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0):
-   ic_device_pebble.png (by xphnx)
+   ic_device_pebble.png (by 9)
    ic_device_miband.png (by xphnx)
    ic_activitytracker.png (by xphnx)
    ic_watchface.png (by xphnx)
 
 Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0):
    "GET IT ON F-Droid" button by Laura Kalbag. Source: https://ind.ie/about/blog/f-droid-button/
+
+Creative Commons Attribution 3.0 Unported license (CC BY-3.0):
+   ic_notification_battery_low.png by Picol.org. Source: https://commons.wikimedia.org/wiki/File:Battery_1_Picol_icon.svg

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/deviceevents/GBDeviceEventBatteryInfo.java

@@ -4,7 +4,7 @@ package nodomain.freeyourgadget.gadgetbridge.deviceevents;
 import java.util.GregorianCalendar;
 
 public class GBDeviceEventBatteryInfo extends GBDeviceEvent {
-    public GregorianCalendar lastChargeTime;
+    public GregorianCalendar lastChargeTime= null;
     public BatteryState state = BatteryState.UNKNOWN;
     //TODO: I think the string should be deprecated in favor of the Enum above
     public String status;
@@ -22,4 +22,11 @@ public class GBDeviceEventBatteryInfo extends GBDeviceEvent {
         CHARGE_LOW,
         CHARGING,
     }
+
+    public boolean extendedInfoAvailable() {
+        if (numCharges != -1 && lastChargeTime != null) {
+            return true;
+        }
+        return false;
+    }
 }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/impl/GBDevice.java

@@ -30,6 +30,7 @@ public class GBDevice implements Parcelable {
     private static final Logger LOG = LoggerFactory.getLogger(GBDevice.class);
     public static final short RSSI_UNKNOWN = 0;
     public static final short BATTERY_UNKNOWN = -1;
+    private static final short BATTERY_THRESHOLD_PERCENT = 10;
     public static final String EXTRA_DEVICE = "device";
     private final String mName;
     private final String mAddress;
@@ -38,6 +39,7 @@ public class GBDevice implements Parcelable {
     private String mHardwareVersion = null;
     private State mState = State.NOT_CONNECTED;
     private short mBatteryLevel = BATTERY_UNKNOWN;
+    private short mBatteryThresholdPercent = BATTERY_THRESHOLD_PERCENT;
     //TODO: get rid of String mBatteryStatus in favor of Enum mBatteryState
     private String mBatteryStatus;
     private short mRssi = RSSI_UNKNOWN;
@@ -293,6 +295,15 @@ public class GBDevice implements Parcelable {
         mBatteryStatus = batteryStatus;
     }
 
+
+    public short getBatteryThresholdPercent() {
+        return mBatteryThresholdPercent;
+    }
+
+    public void setBatteryThresholdPercent(short batteryThresholdPercent) {
+        this.mBatteryThresholdPercent = batteryThresholdPercent;
+    }
+
     @Override
     public String toString() {
         return "Device " + getName() + ", " + getAddress() + ", " + getStateString();

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/AbstractDeviceSupport.java

@@ -230,12 +230,13 @@ public abstract class AbstractDeviceSupport implements DeviceSupport {
         gbDevice.setBatteryLevel(deviceEvent.level);
         gbDevice.setBatteryStatus(deviceEvent.status);
 
-
+        if (deviceEvent.level <= gbDevice.getBatteryThresholdPercent()) {
-        //TODO: maybe switch to a device-dependent threshold
+            GB.updateBatteryNotification(context.getString(R.string.notif_battery_low_percent, gbDevice.getName(), deviceEvent.level),
-        if (deviceEvent.level < 10) {
+                    deviceEvent.extendedInfoAvailable() ?
-            GB.updateBatteryNotification(deviceEvent.level,
+                            context.getString(R.string.notif_battery_low_percent, gbDevice.getName(), deviceEvent.level) + "\n" +
-                    context.getString(R.string.notif_battery_low_bigtext_last_charge_time, DateFormat.getDateTimeInstance().format(deviceEvent.lastChargeTime.getTime()).toString()) +
+                            context.getString(R.string.notif_battery_low_bigtext_last_charge_time, DateFormat.getDateTimeInstance().format(deviceEvent.lastChargeTime.getTime()).toString()) +
                             context.getString(R.string.notif_battery_low_bigtext_number_of_charges, deviceEvent.numCharges)
+                            : ""
                     , context);
         }
 

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/GB.java

@@ -300,7 +300,7 @@ public class GB {
         nm.notify(NOTIFICATION_ID_INSTALL, notification);
     }
 
-    private static Notification createBatteryNotification(int level, String text, Context context) {
+    private static Notification createBatteryNotification(String text, String bigText, Context context) {
         Intent notificationIntent = new Intent(context, ControlCenter.class);
         notificationIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                 | Intent.FLAG_ACTIVITY_CLEAR_TASK);
@@ -308,18 +308,22 @@ public class GB {
                 notificationIntent, 0);
 
         NotificationCompat.Builder nb = new NotificationCompat.Builder(context)
-                .setContentTitle(context.getString(R.string.notif_battery_low_title))
+                .setContentTitle( context.getString(R.string.notif_battery_low_title))
-                .setContentText(context.getString(R.string.notif_battery_low_percent, level))
+                .setContentText(text)
                 .setContentIntent(pendingIntent)
-                .setSmallIcon(R.drawable.ic_notification)
+                .setSmallIcon(R.drawable.ic_notification_low_battery)
-                .setStyle(new NotificationCompat.BigTextStyle().bigText(text))
+                .setPriority(NotificationCompat.PRIORITY_HIGH)
                 .setOngoing(false);
 
+        if (bigText != null) {
+            nb.setStyle(new NotificationCompat.BigTextStyle().bigText(bigText));
+        }
+
         return nb.build();
     }
 
-    public static void updateBatteryNotification(int level, String text, Context context) {
+    public static void updateBatteryNotification(String text, String bigText, Context context) {
-        Notification notification = createBatteryNotification(level, text, context);
+        Notification notification = createBatteryNotification(text, bigText, context);
 
         NotificationManager nm = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
         nm.notify(NOTIFICATION_ID_LOW_BATTERY, notification);

app/src/main/res/values/strings.xml

@@ -167,7 +167,7 @@
     <string name="pbw_install_handler_hw_revision_mismatch">Unable to install the given firmware: it doesn\'t match your Pebble\'s hardware revision.</string>
     <string name="installer_activity_wait_while_determining_status">Please wait while determining the installation status...</string>
     <string name="notif_battery_low_title">Gadget battery Low!</string>
-    <string name="notif_battery_low_percent">Battery left: %s%%</string>
+    <string name="notif_battery_low_percent">%1$s battery left: %2$s%%</string>
     <string name="notif_battery_low_bigtext_last_charge_time">Last charge: %s \n</string>
     <string name="notif_battery_low_bigtext_number_of_charges">Number of charges: %s</string>
 </resources>