Adding callback back to battery read to fix clearing the characteristicChanged callback by accident.

src/extensions/scratch3_wedo2/index.js

@@ -787,7 +787,9 @@ class WeDo2 {
     _checkBatteryLevel () {
         this._ble.read(
             BLEService.DEVICE_SERVICE,
-            BLECharacteristic.LOW_VOLTAGE_ALERT
+            BLECharacteristic.LOW_VOLTAGE_ALERT,
+            false,
+            this._onMessage
         );
     }
 

src/io/ble.js

@@ -80,7 +80,7 @@ class BLE extends JSONRPCWebSocket {
         if (this._discoverTimeoutID) {
             window.clearTimeout(this._discoverTimeoutID);
         }
-        
+
         this._runtime.emit(this._runtime.constructor.PERIPHERAL_DISCONNECT);
     }