added low battery message

src/components/battery/BatteryController.cpp

@@ -88,10 +88,16 @@ void Battery::SaadcEventHandler(nrfx_saadc_evt_t const* p_event) {
 
     if ((isPowerPresent && newPercent > percentRemaining) || (!isPowerPresent && newPercent < percentRemaining) || firstMeasurement) {
       firstMeasurement = false;
+      lastPercentRemaining = percentRemaining;
       percentRemaining = newPercent;
       systemTask->PushMessage(System::Messages::BatteryPercentageUpdated);
     }
 
+    constexpr uint8_t lowBatteryThreshold {50};
+    if (!isPowerPresent && lastPercentRemaining >= lowBatteryThreshold && percentRemaining < lowBatteryThreshold) {
+      systemTask->PushMessage(System::Messages::LowBattery);
+    }
+
     nrfx_saadc_uninit();
     isReading = false;
   }

src/components/battery/BatteryController.h

@@ -39,6 +39,7 @@ namespace Pinetime {
       static constexpr nrf_saadc_input_t batteryVoltageAdcInput = NRF_SAADC_INPUT_AIN7;
       uint16_t voltage = 0;
       uint8_t percentRemaining = 0;
+      uint8_t lastPercentRemaining = 0;
 
       bool isFull = false;
       bool isCharging = false;

src/systemtask/Messages.h

@@ -29,6 +29,7 @@ namespace Pinetime {
       StopRinging,
       MeasureBatteryTimerExpired,
       BatteryPercentageUpdated,
+      LowBattery,
       StartFileTransfer,
       StopFileTransfer,
       BleRadioEnableToggle

src/systemtask/SystemTask.cpp

@@ -424,6 +424,17 @@ void SystemTask::Work() {
         case Messages::BatteryPercentageUpdated:
           nimbleController.NotifyBatteryLevel(batteryController.PercentRemaining());
           break;
+        case Messages::LowBattery:
+          {
+            Pinetime::Controllers::NotificationManager::Notification notif;
+            std::array<char, 101> message {"Low Battery\0Low Battery\0"};
+            notif.message = message; 
+            notif.size = 25;
+            notif.category = Pinetime::Controllers::NotificationManager::Categories::SimpleAlert;
+            notificationManager.Push(std::move(notif));
+            PushMessage(Messages::OnNewNotification);
+          }
+          break;
         case Messages::OnPairing:
           if (state == SystemTaskState::Sleeping) {
             GoToRunning();