Rover: fixed BattMonitor initialisation

APMrover2/APMrover2.pde

@@ -545,8 +545,6 @@ void setup() {
 
     notify.init(false);
 
-    battery.init();
-
     rssi_analog_source = hal.analogin->channel(ANALOG_INPUT_NONE);
 
 	init_ardupilot();

APMrover2/system.pde

@@ -93,6 +93,8 @@ static void init_ardupilot()
 
     set_control_channels();
 
+    battery.init();
+
     // keep a record of how many resets have happened. This can be
     // used to detect in-flight resets
     g.num_resets.set_and_save(g.num_resets+1);