Simulator: virtual battery drain stops by default at 50% to avoid failing...

Simulator: virtual battery drain stops by default at 50% to avoid failing preflight checks to take off again
also added comments and removed throttle compensation because there is no real battery emulation with load drop

src/modules/simulator/simulator_mavlink.cpp

@@ -368,14 +368,16 @@ void Simulator::handle_message(mavlink_message_t *msg, bool publish)
 					batt_sim_start = now;
 				}
 
-				float ibatt = -1.0f;
+				float ibatt = -1.0f; // no current sensor in simulation
+				const float minimum_percentage = 0.5f; // change this value if you want to simulate low battery reaction
 
-				const float battery_time = (now - batt_sim_start) / discharge_interval_us;
-				float vbatt = math::gradual(battery_time, 0.f, 1.f, _battery.full_cell_voltage(), _battery.empty_cell_voltage());
+				/* Simulate the voltage of a linearly draining battery but stop at the minimum percentage */
+				float battery_percentage = (now - batt_sim_start) / discharge_interval_us;
+				battery_percentage = math::min(battery_percentage, minimum_percentage);
+				float vbatt = math::gradual(battery_percentage, 0.f, 1.f, _battery.full_cell_voltage(), _battery.empty_cell_voltage());
 				vbatt *= _battery.cell_count();
 
-				// TODO: don't hard-code throttle.
-				const float throttle = 0.5f;
+				const float throttle = 0.0f; // simulate no throttle compensation to make the estimate predictable
 				_battery.updateBatteryStatus(now, vbatt, ibatt, true, true, 0, throttle, armed, &_battery_status);
 
 				// publish the battery voltage