Plane: added 2nd battery monitoring support

ArduPlane/GCS_Mavlink.pde

@@ -634,6 +634,11 @@ bool GCS_MAVLINK::try_send_message(enum ap_message id)
 #endif
         break;
 
+    case MSG_BATTERY2:
+        CHECK_PAYLOAD_SIZE(BATTERY2);
+        gcs[chan-MAVLINK_COMM_0].send_battery2(battery);
+        break;
+
     case MSG_WIND:
         CHECK_PAYLOAD_SIZE(WIND);
         send_wind(chan);
@@ -870,6 +875,7 @@ GCS_MAVLINK::data_stream_send(void)
 #if AP_TERRAIN_AVAILABLE
         send_message(MSG_TERRAIN);
 #endif
+        send_message(MSG_BATTERY2);
     }
 }