batteryCheck: add new battery threshold for arming (COM_ARM_BAT_MIN)

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

src/modules/commander/HealthAndArmingChecks/checks/batteryCheck.cpp

@@ -95,6 +95,7 @@ void BatteryChecks::checkAndReport(const Context &context, Report &reporter)
 	// option is to check if ANY of them have a warning, and specifically find which one has the most
 	// urgent warning.
 	uint8_t worst_warning = battery_status_s::BATTERY_WARNING_NONE;
+	float worst_battery_remaining = 1.f;
 	// To make sure that all connected batteries are being regularly reported, we check which one has the
 	// oldest timestamp.
 	hrt_abstime oldest_update = hrt_absolute_time();
@@ -154,6 +155,10 @@ void BatteryChecks::checkAndReport(const Context &context, Report &reporter)
 				worst_warning = battery.warning;
 			}
 
+			if (battery.remaining < worst_battery_remaining) {
+				worst_battery_remaining = battery.remaining;
+			}
+
 			if (battery.timestamp < oldest_update) {
 				oldest_update = battery.timestamp;
 			}
@@ -223,8 +228,25 @@ void BatteryChecks::checkAndReport(const Context &context, Report &reporter)
 		if (reporter.mavlink_log_pub()) {
 			mavlink_log_emergency(reporter.mavlink_log_pub(), "Low battery level\t");
 		}
-		}
 
+	} else if (!context.isArmed() && _param_arm_battery_level_min.get() > FLT_EPSILON
+		   && worst_battery_remaining < _param_arm_battery_level_min.get()) {
+		// if not armed, additionally check if the battery is below the separately configurable preflight threshold
+		/* EVENT
+		 * @description
+		 * The battery state of charge of the worst battery is below the preflight threshold.
+		 *
+		 * <profile name="dev">
+		 * This check can be configured via <param>COM_ARM_BAT_MIN</param> parameter.
+		 * </profile>
+		 */
+		reporter.armingCheckFailure(NavModes::All, health_component_t::battery, events::ID("check_battery_preflight_low"),
+					    events::Log::Critical,
+					    "Low battery");
+
+		if (reporter.mavlink_log_pub()) {
+			mavlink_log_emergency(reporter.mavlink_log_pub(), "Low battery level\t");
+		}
 	}
 
 	rtlEstimateCheck(context, reporter, worst_battery_time_s);

src/modules/commander/HealthAndArmingChecks/checks/batteryCheck.hpp

@@ -56,4 +56,7 @@ private:
 	bool _last_armed{false};
 	bool _battery_connected_at_arming[battery_status_s::MAX_INSTANCES] {};
 
+	DEFINE_PARAMETERS_CUSTOM_PARENT(HealthAndArmingCheckBase,
+					(ParamFloat<px4::params::COM_ARM_BAT_MIN>) _param_arm_battery_level_min
+				       )
 };

src/modules/commander/commander_params.c

@@ -1098,3 +1098,20 @@ PARAM_DEFINE_FLOAT(COM_POS_LOW_EPH, -1.0f);
  * @group Commander
  */
 PARAM_DEFINE_INT32(COM_ARMABLE, 1);
+
+/**
+ * Minimum battery level for arming
+ *
+ * Additional battery level check that only allows arming if the state of charge of the emptiest
+ *  connected battery is above this value.
+ *
+ * A value of 0 disables the check.
+ *
+ * @unit norm
+ * @min 0
+ * @max 0.9
+ * @decimal 2
+ * @increment 0.01
+ * @group Commander
+ */
+PARAM_DEFINE_FLOAT(COM_ARM_BAT_MIN, 0.f);