Add critical battery setting for PX4

src/AutoPilotPlugins/PX4/SafetyComponent.qml

@@ -117,7 +117,7 @@ QGCView {
                                 QGCLabel {
                                     anchors.baseline:   batLowLevelField.baseline
                                     width:              _middleRowWidth
-                                    text:               qsTr("Battery Low Level:")
+                                    text:               qsTr("Battery Warn Level:")
                                 }
                                 FactTextField {
                                     id:                 batLowLevelField
@@ -126,6 +126,19 @@ QGCView {
                                     width:              _editFieldWidth
                                 }
                             }
+                            Row {
+                                QGCLabel {
+                                    anchors.baseline:   batLowLevelField.baseline
+                                    width:              _middleRowWidth
+                                    text:               qsTr("Battery Failsafe Level:")
+                                }
+                                FactTextField {
+                                    id:                 batCritLevelField
+                                    fact:               controller.getParameterFact(-1, "BAT_CRIT_THR")
+                                    showUnits:          true
+                                    width:              _editFieldWidth
+                                }
+                            }
                         }
                     }
                 }