AP_Logger: only log Battery Status for active monitors

libraries/AP_Logger/LogFile.cpp

@@ -655,11 +655,14 @@ void AP_Logger::Write_Current_instance(const uint64_t time_us,
 // Write an Current data packet
 void AP_Logger::Write_Current()
 {
+    AP_BattMonitor &battery = AP::battery();
     const uint64_t time_us = AP_HAL::micros64();
     const uint8_t num_instances = AP::battery().num_instances();
     for (uint8_t i = 0; i < num_instances; i++) {
+        if (battery.get_type(i) != AP_BattMonitor::Type::NONE) {
             Write_Current_instance(time_us, i);
         }
+    }
 }
 
 void AP_Logger::Write_Compass_instance(const uint64_t time_us, const uint8_t mag_instance)