bat_sim: parameter for disabling battery simulator

ROMFS/px4fmu_common/init.d-posix/rcS

@@ -248,7 +248,12 @@ then
 fi
 
 load_mon start
-battery_simulator start
+
+if param compare SIM_BAT_ENABLE 1
+then
+	battery_simulator start
+fi
+
 tone_alarm start
 rc_update start
 manual_control start

src/modules/simulation/battery_simulator/battery_simulator_params.c

@@ -31,6 +31,18 @@
  *
  ****************************************************************************/
 
+/**
+ * Simulator Battery enabled
+ *
+ * Enable or disable the internal battery simulation. This is useful
+ * when the battery is simulated externally and interfaced with PX4
+ * through MAVLink for example.
+ *
+ * @boolean
+ * @group SITL
+ */
+PARAM_DEFINE_INT32(SIM_BAT_ENABLE, 1);
+
 /**
  * Simulator Battery drain interval
  *