jetson/ros2_ws/src/saltybot_bridge/config/battery_params.yaml

@@ -0,0 +1,24 @@
+# battery_params.yaml — Battery management node configuration (Issue #125)
+
+# ── SQLite history ─────────────────────────────────────────────────────────────
+db_path: /var/log/saltybot/battery.db
+history_retention_days: 7      # delete records older than N days
+
+# ── Battery pack ──────────────────────────────────────────────────────────────
+cell_count: 3                  # 3S LiPo (11.1V nominal, 12.6V full)
+
+# ── SoC alert thresholds ──────────────────────────────────────────────────────
+warn_pct:       20.0           # WARNING:   reduce speed to warn_speed_factor
+critical_pct:   10.0           # CRITICAL:  reduce speed to critical_speed_factor
+emergency_pct:   5.0           # EMERGENCY: full stop + disarm
+
+# ── Speed reduction factors (0.0 = stop, 1.0 = no reduction) ─────────────────
+warn_speed_factor:      0.6    # 60% of normal speed at WARNING
+critical_speed_factor:  0.3    # 30% of normal speed at CRITICAL
+
+# ── Charging detection ────────────────────────────────────────────────────────
+# current_ma below this value → charging detected
+charge_detect_ma: -100        # -100 mA threshold (small negative allowed for noise)
+
+# ── Publish rate ──────────────────────────────────────────────────────────────
+publish_rate_hz: 1.0           # /saltybot/battery publish frequency

jetson/ros2_ws/src/saltybot_bridge/launch/battery.launch.py

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+"""battery.launch.py — Launch the battery management node (Issue #125).
+
+Usage:
+  ros2 launch saltybot_bridge battery.launch.py
+
+  # Custom thresholds:
+  ros2 launch saltybot_bridge battery.launch.py \
+    warn_pct:=25.0 critical_pct:=12.0 emergency_pct:=6.0
+
+  # Custom DB path:
+  ros2 launch saltybot_bridge battery.launch.py \
+    db_path:=/mnt/nvme/saltybot/battery.db
+"""
+
+import os
+from ament_index_python.packages import get_package_share_directory
+from launch import LaunchDescription
+from launch.actions import DeclareLaunchArgument
+from launch.substitutions import LaunchConfiguration
+from launch_ros.actions import Node
+
+
+def generate_launch_description() -> LaunchDescription:
+    pkg = get_package_share_directory("saltybot_bridge")
+    params_file = os.path.join(pkg, "config", "battery_params.yaml")
+
+    return LaunchDescription([
+        DeclareLaunchArgument("db_path",               default_value="/var/log/saltybot/battery.db"),
+        DeclareLaunchArgument("cell_count",            default_value="3"),
+        DeclareLaunchArgument("warn_pct",              default_value="20.0"),
+        DeclareLaunchArgument("critical_pct",          default_value="10.0"),
+        DeclareLaunchArgument("emergency_pct",         default_value="5.0"),
+        DeclareLaunchArgument("warn_speed_factor",     default_value="0.6"),
+        DeclareLaunchArgument("critical_speed_factor", default_value="0.3"),
+        DeclareLaunchArgument("charge_detect_ma",      default_value="-100"),
+        DeclareLaunchArgument("publish_rate_hz",       default_value="1.0"),
+
+        Node(
+            package="saltybot_bridge",
+            executable="battery_node",
+            name="battery_node",
+            output="screen",
+            emulate_tty=True,
+            parameters=[
+                params_file,
+                {
+                    "db_path":               LaunchConfiguration("db_path"),
+                    "cell_count":            LaunchConfiguration("cell_count"),
+                    "warn_pct":              LaunchConfiguration("warn_pct"),
+                    "critical_pct":          LaunchConfiguration("critical_pct"),
+                    "emergency_pct":         LaunchConfiguration("emergency_pct"),
+                    "warn_speed_factor":     LaunchConfiguration("warn_speed_factor"),
+                    "critical_speed_factor": LaunchConfiguration("critical_speed_factor"),
+                    "charge_detect_ma":      LaunchConfiguration("charge_detect_ma"),
+                    "publish_rate_hz":       LaunchConfiguration("publish_rate_hz"),
+                },
+            ],
+        ),
+    ])

jetson/ros2_ws/src/saltybot_bridge/saltybot_bridge/battery_node.py

@@ -0,0 +1,409 @@
+"""battery_node.py — Battery management for saltybot (Issue #125).
+
+Subscribes to /saltybot/telemetry/battery (JSON from stm32_cmd_node) and:
+  - Publishes sensor_msgs/BatteryState on /saltybot/battery
+  - Publishes JSON alerts on /saltybot/battery/alert at threshold crossings
+  - Reduces speed limit at low SoC via /saltybot/speed_limit (std_msgs/Float32)
+  - Commands safe stop at critical SoC via /cmd_vel zero + /saltybot/arm False
+  - Logs history to SQLite (default: /var/log/saltybot/battery.db)
+  - Detects charging (current_ma < charge_detect_threshold_ma)
+
+Alert levels (SoC thresholds):
+  20%  WARNING   — reduce max speed to 60%
+  10%  CRITICAL  — reduce max speed to 30%, log prominently
+   5%  EMERGENCY — publish zero /cmd_vel, disarm, log + alert
+
+SoC source priority:
+  1. soc_pct field from STM32 BATTERY telemetry (fuel gauge or lookup on STM32)
+  2. Voltage-based lookup table (3S LiPo curve) if soc_pct == 0 and voltage known
+
+Parameters (config/battery_params.yaml):
+  db_path              /var/log/saltybot/battery.db
+  cell_count           3        (number of LiPo cells)
+  warn_pct             20.0
+  critical_pct         10.0
+  emergency_pct         5.0
+  warn_speed_factor     0.6
+  critical_speed_factor 0.3
+  charge_detect_ma     -100     (current_ma below this → charging)
+  history_retention_days 7
+  publish_rate_hz       1.0     (re-publish rate for /saltybot/battery)
+"""
+
+from __future__ import annotations
+
+import json
+import math
+import os
+import sqlite3
+import time
+from typing import Optional
+
+import rclpy
+from rclpy.node import Node
+from rclpy.qos import HistoryPolicy, QoSProfile, ReliabilityPolicy
+
+from geometry_msgs.msg import Twist
+from sensor_msgs.msg import BatteryState
+from std_msgs.msg import Float32, String
+from std_srvs.srv import SetBool
+
+# ── SoC voltage lookup table (3S LiPo, per-cell voltage → SoC %) ─────────────
+# Based on typical LiPo discharge curve at 1C
+_SOC_CURVE_PER_CELL = [
+    # (cell_v, soc_pct) — sorted ascending by voltage
+    (3.00,  0),
+    (3.27,  5),
+    (3.37, 10),
+    (3.53, 20),
+    (3.62, 30),
+    (3.68, 40),
+    (3.73, 50),
+    (3.78, 60),
+    (3.83, 70),
+    (3.90, 80),
+    (4.00, 90),
+    (4.20, 100),
+]
+
+# Alert level constants
+_ALERT_NONE      = "ok"
+_ALERT_WARN      = "warning"
+_ALERT_CRITICAL  = "critical"
+_ALERT_EMERGENCY = "emergency"
+
+
+def _soc_from_voltage(voltage_v: float, cell_count: int) -> int:
+    """Estimate SoC from pack voltage using per-cell LiPo lookup table."""
+    if cell_count <= 0:
+        return 0
+    cell_v = voltage_v / cell_count
+    curve = _SOC_CURVE_PER_CELL
+
+    if cell_v <= curve[0][0]:
+        return 0
+    if cell_v >= curve[-1][0]:
+        return 100
+
+    # Linear interpolation between adjacent points
+    for i in range(len(curve) - 1):
+        v_lo, soc_lo = curve[i]
+        v_hi, soc_hi = curve[i + 1]
+        if v_lo <= cell_v <= v_hi:
+            t = (cell_v - v_lo) / (v_hi - v_lo)
+            return int(soc_lo + t * (soc_hi - soc_lo))
+    return 0
+
+
+class BatteryNode(Node):
+    """Battery management and monitoring node."""
+
+    def __init__(self) -> None:
+        super().__init__("battery_node")
+
+        # ── Parameters ────────────────────────────────────────────────────────
+        self.declare_parameter("db_path",               "/var/log/saltybot/battery.db")
+        self.declare_parameter("cell_count",            3)
+        self.declare_parameter("warn_pct",              20.0)
+        self.declare_parameter("critical_pct",          10.0)
+        self.declare_parameter("emergency_pct",          5.0)
+        self.declare_parameter("warn_speed_factor",      0.6)
+        self.declare_parameter("critical_speed_factor",  0.3)
+        self.declare_parameter("charge_detect_ma",      -100)
+        self.declare_parameter("history_retention_days", 7)
+        self.declare_parameter("publish_rate_hz",        1.0)
+
+        self._db_path             = self.get_parameter("db_path").value
+        self._cell_count          = self.get_parameter("cell_count").value
+        self._warn_pct            = self.get_parameter("warn_pct").value
+        self._critical_pct        = self.get_parameter("critical_pct").value
+        self._emergency_pct       = self.get_parameter("emergency_pct").value
+        self._warn_speed_factor   = self.get_parameter("warn_speed_factor").value
+        self._critical_speed_factor = self.get_parameter("critical_speed_factor").value
+        self._charge_detect_ma    = self.get_parameter("charge_detect_ma").value
+        self._retention_days      = self.get_parameter("history_retention_days").value
+        publish_rate              = self.get_parameter("publish_rate_hz").value
+
+        # ── QoS ───────────────────────────────────────────────────────────────
+        rel_qos = QoSProfile(
+            reliability=ReliabilityPolicy.RELIABLE,
+            history=HistoryPolicy.KEEP_LAST, depth=10,
+        )
+
+        # ── Publishers ────────────────────────────────────────────────────────
+        self._battery_pub     = self.create_publisher(BatteryState, "/saltybot/battery",       rel_qos)
+        self._alert_pub       = self.create_publisher(String,       "/saltybot/battery/alert",  rel_qos)
+        self._speed_limit_pub = self.create_publisher(Float32,      "/saltybot/speed_limit",    rel_qos)
+        self._cmd_vel_pub     = self.create_publisher(Twist,        "/cmd_vel",                 rel_qos)
+
+        # ── Subscribers ───────────────────────────────────────────────────────
+        self._telem_sub = self.create_subscription(
+            String, "/saltybot/telemetry/battery",
+            self._on_battery_telem, rel_qos,
+        )
+
+        # ── Arm service client (for emergency stop) ───────────────────────────
+        self._arm_client = self.create_client(SetBool, "/saltybot/arm")
+
+        # ── State ─────────────────────────────────────────────────────────────
+        self._last_voltage_v  = 0.0
+        self._last_current_ma = 0
+        self._last_soc_pct    = 100
+        self._last_alert      = _ALERT_NONE
+        self._charging        = False
+        self._emergency_fired = False     # prevent repeated disarm calls
+
+        # ── SQLite history ─────────────────────────────────────────────────────
+        self._db: Optional[sqlite3.Connection] = None
+        self._init_db()
+
+        # ── Timers ────────────────────────────────────────────────────────────
+        self._publish_timer  = self.create_timer(1.0 / publish_rate, self._publish_cb)
+        self._prune_timer    = self.create_timer(3600.0, self._prune_history)  # hourly
+
+        self.get_logger().info(
+            f"battery_node started — warn={self._warn_pct}% "
+            f"critical={self._critical_pct}% "
+            f"emergency={self._emergency_pct}% "
+            f"cells={self._cell_count}"
+        )
+
+    # ── SQLite ────────────────────────────────────────────────────────────────
+
+    def _init_db(self) -> None:
+        """Create the SQLite DB and battery_history table if not present."""
+        try:
+            db_dir = os.path.dirname(self._db_path)
+            if db_dir:
+                os.makedirs(db_dir, exist_ok=True)
+            self._db = sqlite3.connect(
+                self._db_path, check_same_thread=False, timeout=5.0
+            )
+            self._db.execute("""
+                CREATE TABLE IF NOT EXISTS battery_history (
+                    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+                    ts          REAL    NOT NULL,
+                    voltage_v   REAL    NOT NULL,
+                    current_ma  INTEGER NOT NULL,
+                    soc_pct     INTEGER NOT NULL,
+                    charging    INTEGER NOT NULL,
+                    alert_level TEXT    NOT NULL
+                )
+            """)
+            self._db.execute(
+                "CREATE INDEX IF NOT EXISTS idx_ts ON battery_history(ts)"
+            )
+            self._db.commit()
+            self.get_logger().info(f"Battery history DB: {self._db_path}")
+        except Exception as exc:
+            self.get_logger().warn(f"Cannot open battery DB ({exc}) — logging disabled")
+            self._db = None
+
+    def _log_to_db(self, voltage_v: float, current_ma: int,
+                   soc_pct: int, charging: bool, alert: str) -> None:
+        if self._db is None:
+            return
+        try:
+            self._db.execute(
+                "INSERT INTO battery_history(ts,voltage_v,current_ma,soc_pct,charging,alert_level) "
+                "VALUES (?,?,?,?,?,?)",
+                (time.time(), voltage_v, current_ma, soc_pct, int(charging), alert),
+            )
+            self._db.commit()
+        except Exception as exc:
+            self.get_logger().warn(f"Battery DB write error: {exc}")
+
+    def _prune_history(self) -> None:
+        """Delete records older than history_retention_days."""
+        if self._db is None:
+            return
+        try:
+            cutoff = time.time() - self._retention_days * 86400
+            self._db.execute("DELETE FROM battery_history WHERE ts < ?", (cutoff,))
+            self._db.commit()
+        except Exception as exc:
+            self.get_logger().warn(f"Battery DB prune error: {exc}")
+
+    # ── Telemetry receive ─────────────────────────────────────────────────────
+
+    def _on_battery_telem(self, msg: String) -> None:
+        """Parse JSON battery telemetry and update internal state."""
+        try:
+            data = json.loads(msg.data)
+            voltage_mv  = int(data["voltage_mv"])
+            current_ma  = int(data["current_ma"])
+            soc_from_fw = int(data.get("soc_pct", 0))
+        except (json.JSONDecodeError, KeyError, ValueError) as exc:
+            self.get_logger().warn(f"Bad battery telemetry: {exc}")
+            return
+
+        voltage_v = voltage_mv / 1000.0
+        charging  = current_ma < self._charge_detect_ma
+
+        # SoC: prefer firmware value; fall back to voltage curve
+        if soc_from_fw > 0:
+            soc_pct = soc_from_fw
+        else:
+            soc_pct = _soc_from_voltage(voltage_v, self._cell_count)
+
+        self._last_voltage_v  = voltage_v
+        self._last_current_ma = current_ma
+        self._last_soc_pct    = soc_pct
+        self._charging        = charging
+
+        # Check thresholds and act
+        new_alert = self._compute_alert(soc_pct)
+        if new_alert != self._last_alert:
+            self._handle_alert_change(new_alert, soc_pct, voltage_v)
+
+        # Log to SQLite
+        self._log_to_db(voltage_v, current_ma, soc_pct, charging, new_alert)
+
+    # ── Alert handling ────────────────────────────────────────────────────────
+
+    def _compute_alert(self, soc_pct: int) -> str:
+        """Return the current alert level string for a given SoC."""
+        if soc_pct <= self._emergency_pct:
+            return _ALERT_EMERGENCY
+        if soc_pct <= self._critical_pct:
+            return _ALERT_CRITICAL
+        if soc_pct <= self._warn_pct:
+            return _ALERT_WARN
+        return _ALERT_NONE
+
+    def _handle_alert_change(self, new_alert: str, soc_pct: int, voltage_v: float) -> None:
+        """Act on threshold transition."""
+        prev = self._last_alert
+        self._last_alert = new_alert
+
+        msg_text = (
+            f"Battery {new_alert.upper()}: {soc_pct}% SoC / {voltage_v:.2f}V "
+            f"(was {prev})"
+        )
+
+        if new_alert == _ALERT_NONE:
+            # Recovery (e.g., plugged in for charging)
+            self.get_logger().info(f"Battery OK: {soc_pct}% SoC")
+            self._publish_speed_limit(1.0)
+
+        elif new_alert == _ALERT_WARN:
+            self.get_logger().warn(msg_text)
+            self._publish_speed_limit(self._warn_speed_factor)
+
+        elif new_alert == _ALERT_CRITICAL:
+            self.get_logger().error(msg_text)
+            self._publish_speed_limit(self._critical_speed_factor)
+
+        elif new_alert == _ALERT_EMERGENCY:
+            self.get_logger().fatal(msg_text)
+            self._publish_speed_limit(0.0)
+            if not self._emergency_fired:
+                self._emergency_fired = True
+                self._execute_safe_stop()
+
+        # Publish alert message
+        alert_payload = json.dumps({
+            "level":       new_alert,
+            "soc_pct":     soc_pct,
+            "voltage_v":   round(voltage_v, 3),
+            "prev_level":  prev,
+            "ts":          time.time(),
+        })
+        alert_msg      = String()
+        alert_msg.data = alert_payload
+        self._alert_pub.publish(alert_msg)
+
+    def _publish_speed_limit(self, factor: float) -> None:
+        """Publish normalised speed limit factor 0.0–1.0."""
+        msg       = Float32()
+        msg.data  = float(factor)
+        self._speed_limit_pub.publish(msg)
+
+    def _execute_safe_stop(self) -> None:
+        """Send zero /cmd_vel and disarm the STM32."""
+        self.get_logger().fatal("EMERGENCY: publishing zero /cmd_vel and disarming")
+        # Publish zero velocity
+        zero_twist = Twist()
+        self._cmd_vel_pub.publish(zero_twist)
+
+        # Call /saltybot/arm(False) if service is available
+        if self._arm_client.service_is_ready():
+            req          = SetBool.Request()
+            req.data     = False
+            self._arm_client.call_async(req)
+        else:
+            self.get_logger().warn(
+                "/saltybot/arm service not available for emergency disarm"
+            )
+
+    # ── Periodic publish ──────────────────────────────────────────────────────
+
+    def _publish_cb(self) -> None:
+        """Publish sensor_msgs/BatteryState at configured rate."""
+        if self._last_voltage_v == 0.0:
+            return    # no telemetry received yet
+
+        msg = BatteryState()
+        msg.header.stamp    = self.get_clock().now().to_msg()
+        msg.header.frame_id = "battery"
+
+        msg.voltage         = self._last_voltage_v
+        msg.current         = self._last_current_ma / 1000.0    # mA → A
+        msg.percentage      = self._last_soc_pct / 100.0        # 0.0–1.0
+
+        # Capacity: 3S 5000 mAh pack (configurable in future)
+        msg.design_capacity = 5.0   # Ah
+        msg.capacity        = float("nan")
+        msg.charge          = float("nan")
+        msg.temperature     = float("nan")
+
+        if self._charging:
+            msg.power_supply_status = BatteryState.POWER_SUPPLY_STATUS_CHARGING
+        elif self._last_soc_pct >= 99:
+            msg.power_supply_status = BatteryState.POWER_SUPPLY_STATUS_FULL
+        else:
+            msg.power_supply_status = BatteryState.POWER_SUPPLY_STATUS_DISCHARGING
+
+        msg.power_supply_technology = BatteryState.POWER_SUPPLY_TECHNOLOGY_LIPO
+        msg.power_supply_health     = (
+            BatteryState.POWER_SUPPLY_HEALTH_GOOD
+            if self._last_alert in (_ALERT_NONE, _ALERT_WARN)
+            else BatteryState.POWER_SUPPLY_HEALTH_UNSPEC_FAILURE
+        )
+        msg.present = True
+
+        # Cell voltages (estimated, equal distribution assumption)
+        if self._cell_count > 0:
+            cell_v = self._last_voltage_v / self._cell_count
+            msg.cell_voltage = [cell_v] * self._cell_count
+
+        # Location field: alert level for easy monitoring
+        msg.location = self._last_alert
+
+        self._battery_pub.publish(msg)
+
+    # ── Lifecycle ─────────────────────────────────────────────────────────────
+
+    def destroy_node(self) -> None:
+        if self._db:
+            try:
+                self._db.close()
+            except Exception:
+                pass
+        super().destroy_node()
+
+
+def main(args=None) -> None:
+    rclpy.init(args=args)
+    node = BatteryNode()
+    try:
+        rclpy.spin(node)
+    except KeyboardInterrupt:
+        pass
+    finally:
+        node.destroy_node()
+        rclpy.shutdown()
+
+
+if __name__ == "__main__":
+    main()

jetson/ros2_ws/src/saltybot_bridge/test/test_battery.py

@@ -0,0 +1,429 @@
+"""test_battery.py — Unit tests for battery_node SoC, alerts, and SQLite logging.
+
+Tests:
+  - SoC lookup table: known voltages map to expected percentages
+  - SoC interpolation: midpoint between curve entries
+  - SoC clamping: below min → 0%, above max → 100%
+  - Alert level computation: correct level for various SoC values
+  - Alert threshold transitions: NONE→WARN→CRITICAL→EMERGENCY
+  - Speed factor assignments: correct factor per alert level
+  - Charging detection: current_ma < threshold → charging
+  - sensor_msgs/BatteryState field population
+  - SQLite logging: records inserted with correct fields
+  - SQLite pruning: old records removed
+  - Voltage-based SoC fallback when firmware SoC == 0
+  - Multi-cell voltage scaling (3S, 4S)
+
+Run with: pytest test/test_battery.py -v
+No ROS2 runtime required.
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import sqlite3
+import sys
+import tempfile
+import time
+
+import pytest
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
+
+from saltybot_bridge.battery_node import (
+    _soc_from_voltage,
+    _ALERT_NONE, _ALERT_WARN, _ALERT_CRITICAL, _ALERT_EMERGENCY,
+    _SOC_CURVE_PER_CELL,
+)
+
+
+# ═══════════════════════════════════════════════════════════════════
+# SoC voltage lookup table
+# ═══════════════════════════════════════════════════════════════════
+
+class TestSocLookup:
+
+    def test_full_voltage_returns_100(self):
+        """4.20 V/cell (3-cell = 12.60 V) → 100%."""
+        assert _soc_from_voltage(12.60, cell_count=3) == 100
+
+    def test_below_min_returns_0(self):
+        """Below 3.0 V/cell → 0%."""
+        assert _soc_from_voltage(8.0, cell_count=3) == 0
+
+    def test_nominal_voltage_returns_50ish(self):
+        """3S at ~11.1 V (3.7 V/cell) should be near 50%."""
+        soc = _soc_from_voltage(11.10, cell_count=3)
+        assert 45 <= soc <= 55
+
+    def test_warn_threshold_voltage_single_cell(self):
+        """Single-cell 3.53 V is on the 20% curve point."""
+        assert _soc_from_voltage(3.53, cell_count=1) == 20
+
+    def test_critical_threshold_voltage(self):
+        """3.37 V/cell → 10%."""
+        assert _soc_from_voltage(3.37, cell_count=1) == 10
+
+    def test_emergency_threshold_voltage(self):
+        """3.27 V/cell → 5%."""
+        assert _soc_from_voltage(3.27, cell_count=1) == 5
+
+    def test_4s_pack_full(self):
+        """4S fully charged: 4 × 4.20 = 16.80 V → 100%."""
+        assert _soc_from_voltage(16.80, cell_count=4) == 100
+
+    def test_4s_pack_nominal(self):
+        """4S nominal: 4 × 3.7 = 14.8 V → ~50%."""
+        soc = _soc_from_voltage(14.80, cell_count=4)
+        assert 45 <= soc <= 55
+
+    def test_interpolation_midpoint(self):
+        """Midpoint between two curve entries should yield midpoint SoC."""
+        # Between (3.27, 5) and (3.37, 10): midpoint ≈ 3.32 V → ~7.5%
+        mid_v = (3.27 + 3.37) / 2 * 3  # 3-cell pack voltage
+        soc = _soc_from_voltage(mid_v, cell_count=3)
+        assert 5 < soc < 10
+
+    def test_exactly_at_curve_point(self):
+        """Values exactly on a curve point must return the tabulated SoC."""
+        for cell_v, expected_soc in _SOC_CURVE_PER_CELL:
+            pack_v = cell_v * 3   # 3-cell
+            result = _soc_from_voltage(pack_v, cell_count=3)
+            # Allow ±1 for floating-point interpolation edge
+            assert abs(result - expected_soc) <= 1, \
+                f"At {cell_v}V/cell ({pack_v}V 3S): expected {expected_soc}%, got {result}%"
+
+    def test_zero_cell_count_returns_0(self):
+        assert _soc_from_voltage(12.0, cell_count=0) == 0
+
+    def test_above_max_clamped_to_100(self):
+        """Overcharged (e.g., 4.5 V/cell) → clamped to 100%."""
+        assert _soc_from_voltage(15.0, cell_count=3) == 100
+
+    def test_zero_voltage_returns_0(self):
+        assert _soc_from_voltage(0.0, cell_count=3) == 0
+
+    def test_returns_integer(self):
+        result = _soc_from_voltage(11.1, cell_count=3)
+        assert isinstance(result, int)
+
+
+# ═══════════════════════════════════════════════════════════════════
+# Alert level computation
+# ═══════════════════════════════════════════════════════════════════
+
+class TestAlertComputation:
+    """Test _compute_alert() logic (instantiated via a minimal stub)."""
+
+    # Mirror of BatteryNode._compute_alert() for unit testing
+    @staticmethod
+    def _compute_alert(soc_pct, warn=20.0, crit=10.0, emergency=5.0):
+        if soc_pct <= emergency:
+            return _ALERT_EMERGENCY
+        if soc_pct <= crit:
+            return _ALERT_CRITICAL
+        if soc_pct <= warn:
+            return _ALERT_WARN
+        return _ALERT_NONE
+
+    def test_full_is_ok(self):
+        assert self._compute_alert(100) == _ALERT_NONE
+
+    def test_above_warn_is_ok(self):
+        assert self._compute_alert(21) == _ALERT_NONE
+
+    def test_at_warn_threshold(self):
+        assert self._compute_alert(20) == _ALERT_WARN
+
+    def test_between_warn_and_critical(self):
+        assert self._compute_alert(15) == _ALERT_WARN
+
+    def test_at_critical_threshold(self):
+        assert self._compute_alert(10) == _ALERT_CRITICAL
+
+    def test_between_critical_and_emergency(self):
+        assert self._compute_alert(7) == _ALERT_CRITICAL
+
+    def test_at_emergency_threshold(self):
+        assert self._compute_alert(5) == _ALERT_EMERGENCY
+
+    def test_below_emergency(self):
+        assert self._compute_alert(1) == _ALERT_EMERGENCY
+
+    def test_zero_is_emergency(self):
+        assert self._compute_alert(0) == _ALERT_EMERGENCY
+
+    def test_custom_thresholds(self):
+        assert self._compute_alert(25, warn=30, crit=15, emergency=8) == _ALERT_WARN
+        assert self._compute_alert(13, warn=30, crit=15, emergency=8) == _ALERT_WARN
+        assert self._compute_alert(12, warn=30, crit=15, emergency=8) == _ALERT_CRITICAL
+
+    def test_speed_factor_at_warn(self):
+        """Speed factor at WARN must be 0 < factor < 1.0."""
+        factor = 0.6    # warn_speed_factor default
+        assert 0.0 < factor < 1.0
+
+    def test_speed_factor_at_critical(self):
+        factor = 0.3    # critical_speed_factor default
+        assert 0.0 < factor < 1.0
+
+    def test_speed_factor_at_emergency(self):
+        factor = 0.0    # full stop
+        assert factor == 0.0
+
+
+# ═══════════════════════════════════════════════════════════════════
+# Charging detection
+# ═══════════════════════════════════════════════════════════════════
+
+class TestChargingDetection:
+
+    THRESHOLD_MA = -100
+
+    def _is_charging(self, current_ma):
+        return current_ma < self.THRESHOLD_MA
+
+    def test_discharging_positive(self):
+        assert not self._is_charging(500)
+
+    def test_discharging_zero(self):
+        assert not self._is_charging(0)
+
+    def test_just_below_threshold_is_charging(self):
+        assert self._is_charging(-101)
+
+    def test_at_threshold_not_charging(self):
+        assert not self._is_charging(-100)
+
+    def test_deeply_negative_is_charging(self):
+        assert self._is_charging(-2000)    # fast charge
+
+    def test_regen_braking_not_charging(self):
+        # Small negative current during regen isn't real charging
+        assert not self._is_charging(-50)
+
+
+# ═══════════════════════════════════════════════════════════════════
+# SQLite history logging
+# ═══════════════════════════════════════════════════════════════════
+
+class TestSqliteLogging:
+    """Test the SQLite DB operations directly (no ROS2)."""
+
+    def _make_db(self):
+        """Return an in-memory SQLite connection with the battery_history table."""
+        db = sqlite3.connect(":memory:")
+        db.execute("""
+            CREATE TABLE battery_history (
+                id          INTEGER PRIMARY KEY AUTOINCREMENT,
+                ts          REAL    NOT NULL,
+                voltage_v   REAL    NOT NULL,
+                current_ma  INTEGER NOT NULL,
+                soc_pct     INTEGER NOT NULL,
+                charging    INTEGER NOT NULL,
+                alert_level TEXT    NOT NULL
+            )
+        """)
+        db.execute("CREATE INDEX idx_ts ON battery_history(ts)")
+        db.commit()
+        return db
+
+    def _insert(self, db, ts, voltage_v, current_ma, soc_pct, charging, alert):
+        db.execute(
+            "INSERT INTO battery_history(ts,voltage_v,current_ma,soc_pct,charging,alert_level) "
+            "VALUES (?,?,?,?,?,?)",
+            (ts, voltage_v, current_ma, soc_pct, int(charging), alert)
+        )
+        db.commit()
+
+    def test_insert_and_retrieve(self):
+        db = self._make_db()
+        self._insert(db, time.time(), 11.1, 500, 50, False, _ALERT_NONE)
+        row = db.execute("SELECT * FROM battery_history").fetchone()
+        assert row is not None
+        assert row[2] == pytest.approx(11.1)
+        assert row[3] == 500
+        assert row[4] == 50
+        assert row[5] == 0     # not charging
+        assert row[6] == _ALERT_NONE
+
+    def test_insert_charging_event(self):
+        db = self._make_db()
+        self._insert(db, time.time(), 12.0, -1500, 85, True, _ALERT_NONE)
+        row = db.execute("SELECT charging FROM battery_history").fetchone()
+        assert row[0] == 1    # charging = True
+
+    def test_insert_alert_event(self):
+        db = self._make_db()
+        self._insert(db, time.time(), 10.5, 300, 18, False, _ALERT_WARN)
+        row = db.execute("SELECT alert_level FROM battery_history").fetchone()
+        assert row[0] == _ALERT_WARN
+
+    def test_prune_old_records(self):
+        db = self._make_db()
+        old_ts = time.time() - 8 * 86400   # 8 days ago (>7 day retention)
+        new_ts = time.time()
+        self._insert(db, old_ts, 11.0, 100, 60, False, _ALERT_NONE)
+        self._insert(db, new_ts, 11.5, 200, 70, False, _ALERT_NONE)
+
+        retention_days = 7
+        cutoff = time.time() - retention_days * 86400
+        db.execute("DELETE FROM battery_history WHERE ts < ?", (cutoff,))
+        db.commit()
+
+        rows = db.execute("SELECT COUNT(*) FROM battery_history").fetchone()
+        assert rows[0] == 1    # only new record remains
+
+    def test_multiple_inserts_sequential_ids(self):
+        db = self._make_db()
+        for i in range(5):
+            self._insert(db, time.time() + i, 11.0 + i * 0.1, 100, 50 + i, False, _ALERT_NONE)
+        count = db.execute("SELECT COUNT(*) FROM battery_history").fetchone()[0]
+        assert count == 5
+
+    def test_db_on_disk(self):
+        """Write and read a real on-disk SQLite DB."""
+        with tempfile.NamedTemporaryFile(suffix=".db", delete=False) as f:
+            path = f.name
+        try:
+            db = sqlite3.connect(path)
+            db.execute("""CREATE TABLE battery_history (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                ts REAL, voltage_v REAL, current_ma INTEGER,
+                soc_pct INTEGER, charging INTEGER, alert_level TEXT
+            )""")
+            db.execute(
+                "INSERT INTO battery_history VALUES (NULL,?,?,?,?,?,?)",
+                (time.time(), 11.5, 500, 70, 0, _ALERT_NONE)
+            )
+            db.commit()
+            db.close()
+
+            # Reopen and verify
+            db2 = sqlite3.connect(path)
+            row = db2.execute("SELECT soc_pct FROM battery_history").fetchone()
+            assert row[0] == 70
+            db2.close()
+        finally:
+            os.unlink(path)
+
+
+# ═══════════════════════════════════════════════════════════════════
+# BatteryState field population
+# ═══════════════════════════════════════════════════════════════════
+
+class TestBatteryStateFields:
+    """Verify sensor_msgs/BatteryState field logic without a live node."""
+
+    def _make_state(self, voltage_v, current_ma, soc_pct, charging,
+                    cell_count=3, alert=_ALERT_NONE):
+        """Minimal BatteryState-like dict mirrors _publish_cb logic."""
+        return {
+            "voltage":          voltage_v,
+            "current":          current_ma / 1000.0,
+            "percentage":       soc_pct / 100.0,
+            "power_supply_status": "CHARGING" if charging else (
+                "FULL" if soc_pct >= 99 else "DISCHARGING"
+            ),
+            "location":         alert,
+            "cell_voltage":     [voltage_v / cell_count] * cell_count,
+        }
+
+    def test_voltage_field(self):
+        state = self._make_state(11.1, 500, 50, False)
+        assert state["voltage"] == pytest.approx(11.1)
+
+    def test_current_converted_to_amps(self):
+        state = self._make_state(11.1, 1500, 50, False)
+        assert state["current"] == pytest.approx(1.5)
+
+    def test_percentage_normalised(self):
+        state = self._make_state(11.1, 500, 75, False)
+        assert state["percentage"] == pytest.approx(0.75)
+
+    def test_charging_status(self):
+        state = self._make_state(12.0, -1500, 85, True)
+        assert state["power_supply_status"] == "CHARGING"
+
+    def test_discharging_status(self):
+        state = self._make_state(11.1, 500, 50, False)
+        assert state["power_supply_status"] == "DISCHARGING"
+
+    def test_full_status_at_99_pct(self):
+        state = self._make_state(12.5, 0, 99, False)
+        assert state["power_supply_status"] == "FULL"
+
+    def test_cell_voltages_equal_distribution(self):
+        state = self._make_state(12.0, 0, 80, False, cell_count=3)
+        assert len(state["cell_voltage"]) == 3
+        for cv in state["cell_voltage"]:
+            assert cv == pytest.approx(4.0)
+
+    def test_alert_in_location_field(self):
+        state = self._make_state(10.5, 300, 18, False, alert=_ALERT_WARN)
+        assert state["location"] == _ALERT_WARN
+
+    def test_zero_percentage_at_empty(self):
+        state = self._make_state(9.6, 50, 0, False)
+        assert state["percentage"] == pytest.approx(0.0)
+
+    def test_full_percentage(self):
+        state = self._make_state(12.6, 0, 100, False)
+        assert state["percentage"] == pytest.approx(1.0)
+
+
+# ═══════════════════════════════════════════════════════════════════
+# Telemetry JSON parsing
+# ═══════════════════════════════════════════════════════════════════
+
+class TestTelemetryParsing:
+    """Test the JSON parsing logic that the battery_node uses."""
+
+    @staticmethod
+    def _parse(json_str: str, charge_threshold: int = -100):
+        data = json.loads(json_str)
+        voltage_mv  = int(data["voltage_mv"])
+        current_ma  = int(data["current_ma"])
+        soc_from_fw = int(data.get("soc_pct", 0))
+        voltage_v   = voltage_mv / 1000.0
+        charging    = current_ma < charge_threshold
+        soc_pct     = soc_from_fw if soc_from_fw > 0 else \
+                      _soc_from_voltage(voltage_v, cell_count=3)
+        return voltage_v, current_ma, soc_pct, charging
+
+    def test_normal_discharge_telemetry(self):
+        v, i, soc, chg = self._parse(
+            '{"voltage_mv":11100,"current_ma":1000,"soc_pct":55}'
+        )
+        assert v   == pytest.approx(11.1)
+        assert i   == 1000
+        assert soc == 55      # from firmware
+        assert not chg
+
+    def test_charging_telemetry(self):
+        v, i, soc, chg = self._parse(
+            '{"voltage_mv":12000,"current_ma":-1500,"soc_pct":80}'
+        )
+        assert v   == pytest.approx(12.0)
+        assert i   == -1500
+        assert chg
+
+    def test_firmware_soc_zero_uses_voltage_curve(self):
+        """If soc_pct == 0, fall back to voltage curve."""
+        v, i, soc, chg = self._parse(
+            '{"voltage_mv":11100,"current_ma":500,"soc_pct":0}'
+        )
+        # soc_pct=0 from firmware → use voltage 11.1V / 3 cells → ~50%
+        assert 45 <= soc <= 55
+
+    def test_missing_soc_falls_back_to_voltage(self):
+        """soc_pct field absent → use voltage lookup."""
+        v, i, soc, chg = self._parse(
+            '{"voltage_mv":10500,"current_ma":300}'
+        )
+        assert soc < 25    # 10.5V (3.5V/cell) → ~20%
+
+    def test_parse_error_on_missing_fields(self):
+        with pytest.raises(KeyError):
+            self._parse('{"current_ma":500}')    # missing voltage_mv