refactor(battery_simulator): clean up param SIM_BAT_ENABLE (#26823)

* refactor(battery_simulator): remove SIM_BAT_ENABLE

disable instead with SIM_BAT_DRAIN <= 0

* fix(battery_simulator): disable battery sim only if SIM_BAT_DRAIN strictly < 0

* fix(battery_simulator): disable if 0, adjust limit to 0

* fix(battery_simulator): remove constraining again

now that SIM_BAT_DRAIN=0 means the module is not started we are safe
from division by zero again (param compare has a tolerance of 1e-7)

* fix(battery_simulator): constrain param to min of 1

to avoid division by zero.

This reverts commit 6380c4fdee.

* fix(battery_simulator): remove arbitrary param max

* fix(battery_simulator): reword long param description

Co-authored-by: Jacob Dahl <37091262+dakejahl@users.noreply.github.com>

* fix(battery_simulator): reword short param description

Co-authored-by: Jacob Dahl <37091262+dakejahl@users.noreply.github.com>

---------

Co-authored-by: Jacob Dahl <37091262+dakejahl@users.noreply.github.com>

ROMFS/px4fmu_common/init.d-posix/rcS

@@ -249,7 +249,7 @@ fi
 
 load_mon start
 
-if param compare SIM_BAT_ENABLE 1
+if param greater SIM_BAT_DRAIN 0
 then
 	battery_simulator start
 fi

docs/en/simulation/failsafes.md

@@ -47,7 +47,7 @@ To control how fast the battery depletes to the minimal value use the parameter
 By changing [SIM_BAT_MIN_PCT](../advanced_config/parameter_reference.md#SIM_BAT_MIN_PCT) in flight, you can also test regaining capacity to simulate inaccurate battery state estimation or in-air charging technology.
 :::
 
-It is also possible to disable the simulated battery using [SIM_BAT_ENABLE](../advanced_config/parameter_reference.md#SIM_BAT_ENABLE) in order to, for example, provide an external battery simulation via MAVLink.
+The simulated battery can be completely disabled by setting [SIM_BAT_DRAIN](../advanced_config/parameter_reference.md#SIM_BAT_DRAIN) to 0. This is useful, for example, if you provide an external battery simulation via MAVLink.
 
 ## Sensor/System Failure
 

src/modules/simulation/battery_simulator/BatterySimulator.cpp

@@ -85,7 +85,8 @@ void BatterySimulator::Run()
 
 	const hrt_abstime now_us = hrt_absolute_time();
 
-	const float discharge_interval_us = _param_sim_bat_drain.get() * 1000 * 1000;
+	// Limit to +1.0 s to guard against division by 0
+	const float discharge_interval_us = math::max(_param_sim_bat_drain.get(), 1.0f) * 1000 * 1000;
 
 	if (_armed) {
 		if (_last_integration_us != 0) {

src/modules/simulation/battery_simulator/battery_simulator_params.yaml

@@ -2,22 +2,14 @@ module_name: battery_simulator
 parameters:
 - group: SITL
   definitions:
-    SIM_BAT_ENABLE:
-      description:
-        short: Simulator Battery enabled
-        long: |-
-          Enable or disable the internal battery simulation. This is useful
-          when the battery is simulated externally and interfaced with PX4
-          through MAVLink for example.
-      type: boolean
-      default: 1
     SIM_BAT_DRAIN:
       description:
-        short: Simulator Battery drain interval
+        short: Simulated battery full-discharge time
+        long: |-
+          Time in seconds for the simulated battery to drain from 100% to 0% while armed. Set to 0 to disable the battery simulator entirely (useful when battery state is provided externally, e.g. via MAVLink).
       type: float
       default: 60
-      min: 1
-      max: 86400
+      min: 0
       increment: 1
       unit: s
     SIM_BAT_MIN_PCT: