Add MQTT monitor with Home Assistant autodiscovery

Poll lifepo4wered-cli every 30s (configurable), publish all registers as
one JSON state payload, and announce sensors/binary sensor via MQTT
discovery. run.sh pulls broker credentials from the Supervisor mqtt
service (Mosquitto addon) with manual overrides in addon options.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -1,5 +1,37 @@
 # hassio-addon-lifepo4wered
 
+Home Assistant OS addon for the [LiFePO4wered/Pi+](https://lifepo4wered.com/lifepo4wered-pi+.html)
+UPS: runs `lifepo4wered-daemon` and publishes UPS stats to MQTT with Home
+Assistant autodiscovery.
+
+## MQTT monitor
+
+`lifepo4wered_monitor.py` polls `lifepo4wered-cli get` (default every 30 s)
+and publishes all registers as one JSON payload to `lifepo4wered/state`.
+Entities appear automatically under one device, "LiFePO4wered/Pi+":
+
+- **Sensors**: input/battery/output voltage (V), output current (A)
+- **Binary sensor** "External power": ON when `VIN >= VIN_THRESHOLD`
+  (i.e. OFF means running on battery)
+- **Diagnostics**: thresholds, timers, watchdog and state registers
+- **Availability**: `lifepo4wered/availability` with MQTT Last Will, so
+  entities go *unavailable* if the addon stops
+
+MQTT connection details are taken automatically from the Supervisor when the
+Mosquitto addon is installed. Addon options: `poll_interval` (seconds) and
+optional `mqtt_host`/`mqtt_port`/`mqtt_user`/`mqtt_password` overrides.
+
+### Testing off the Pi
+
+```
+python3 -m unittest discover -s tests            # unit tests, no deps needed
+LIFEPO4WERED_FAKE=1 MQTT_HOST=... python3 hassio-addon-lifepo4wered/lifepo4wered_monitor.py
+```
+
+`LIFEPO4WERED_FAKE=1` replaces the CLI with embedded sample data.
+
+## Setup notes
+
 
 https://www.linkedin.com/pulse/creating-your-first-home-assistant-add-on-issac-goldstand
 

docs/superpowers/specs/2026-07-18-mqtt-monitor-design.md

@@ -0,0 +1,65 @@
+# LiFePO4wered MQTT Monitor — Design
+
+Date: 2026-07-18. Approved by vaku in conversation.
+
+## Goal
+
+Publish LiFePO4wered/Pi+ UPS stats from the Home Assistant OS addon to MQTT,
+with Home Assistant autodiscovery, so the UPS shows up as a device with sensors.
+
+## Approach
+
+A single Python script (`lifepo4wered_monitor.py`) inside the existing addon
+container. It shells out to `lifepo4wered-cli get` (already built into the
+image), parses the `KEY = value` output, and publishes to MQTT via `paho-mqtt`.
+Bindings via ctypes/PyPI were considered and rejected: the CLI is already
+present and one subprocess call reads everything at once.
+
+## Behavior
+
+- Poll every `POLL_INTERVAL` seconds (default 30).
+- One retained JSON state payload per cycle on `lifepo4wered/state`; all
+  entities read it with `value_template` — one MQTT message per cycle.
+- Discovery configs (retained) on `<DISCOVERY_PREFIX>/<component>/lifepo4wered/<key>/config`,
+  republished on every (re)connect. All entities belong to one HA device
+  ("LiFePO4wered/Pi+", manufacturer Silicognition LLC).
+- Main sensors: VIN, VBAT, VOUT (mV → V, device_class `voltage`),
+  IOUT (mA → A, device_class `current`).
+- Binary sensor "External power" (device_class `power`):
+  `VIN >= VIN_THRESHOLD` → ON.
+- Diagnostic entities (`entity_category: diagnostic`): threshold/config
+  registers (VBAT_MIN, VBAT_SHDN, VBAT_BOOT, VOUT_MAX, VIN_THRESHOLD scaled to
+  V; timers, watchdog, AUTO_BOOT, LED_STATE, TOUCH_STATE, PI_RUNNING raw;
+  RTC_TIME as timestamp).
+- Skipped: identity/calibration registers (I2C_REG_VER, I2C_ADDRESS, DCO_*,
+  TOUCH_CAP_CYCLES/THRESHOLD/HYSTERESIS, *_OFFSET, CFG_WRITE, RTC_WAKE_TIME,
+  WAKE_TIME).
+- Availability: MQTT LWT on `lifepo4wered/availability` (`online`/`offline`).
+  CLI failure (I2C hiccup): log, publish `offline`, retry next cycle.
+- Config via env vars: MQTT_HOST, MQTT_PORT, MQTT_USER, MQTT_PASSWORD,
+  POLL_INTERVAL, DISCOVERY_PREFIX, MQTT_TOPIC_PREFIX.
+- `LIFEPO4WERED_FAKE=1` uses embedded sample output instead of the CLI, for
+  testing off the Pi.
+
+## Addon integration
+
+- Dockerfile: add `python3` + `py3-paho-mqtt` (Alpine packages), copy script
+  and `run.sh`, `CMD ["/run.sh"]`.
+- `run.sh` (bashio): pull MQTT host/port/user/password from Supervisor
+  services API (works out of the box with the Mosquitto addon), allow
+  overrides from addon options, start `lifepo4wered-daemon -f` in the
+  background, run the monitor in the foreground.
+- `config.json`: add `"services": ["mqtt:need"]`, addon options
+  (`poll_interval`, optional MQTT overrides), bump version.
+
+## Error handling
+
+- paho built-in reconnect for broker drops; discovery republished on connect.
+- 10 s subprocess timeout on the CLI; malformed lines skipped with a warning.
+- Script compatible with paho-mqtt 1.x and 2.x callback APIs.
+
+## Testing
+
+- Unit tests (stdlib `unittest`) for output parsing and discovery payload
+  generation, runnable on any machine without paho or a broker.
+- Fake mode for end-to-end runs against a real broker off the Pi.

hassio-addon-lifepo4wered/Dockerfile

@@ -9,11 +9,13 @@ FROM homeassistant/aarch64-base:latest
 ENV LANG C.UTF-8
 
 WORKDIR /
+RUN apk add --no-cache python3 py3-paho-mqtt
 COPY --from=build /tmp/LiFePO4wered-Pi/build/liblifepo4wered.so /usr/lib/liblifepo4wered.so
 COPY --from=build /tmp/LiFePO4wered-Pi/build/lifepo4wered-cli /usr/bin/lifepo4wered-cli
 COPY --from=build /tmp/LiFePO4wered-Pi/build/lifepo4wered-daemon /usr/sbin/lifepo4wered-daemon
-# COPY start.sh /app/start.sh
-# ENTRYPOINT ["/app/start.sh"]
-CMD lifepo4wered-daemon -f
+COPY lifepo4wered_monitor.py /usr/bin/lifepo4wered_monitor.py
+COPY run.sh /run.sh
+RUN chmod a+x /run.sh
+CMD ["/run.sh"]
 
 LABEL io.hass.version="VERSION" io.hass.type="addon" io.hass.arch="aarch64"

hassio-addon-lifepo4wered/config.json

@@ -1,14 +1,22 @@
 {
   "name": "LiFePO4wered Addon",
-  "version": "0.0.5",
+  "version": "0.1.0",
   "slug": "lifepo4wered",
-  "description": "Add-on with service for LiFePO4Wered Pi+ UPS",
+  "description": "Add-on with service and MQTT monitor for LiFePO4wered/Pi+ UPS",
   "url": "https://github.com/vakius/hassio-addon-lifepo4wered/tree/master/hassio-addon-lifepo4wered",
   "startup": "application",
   "boot": "auto",
-  "options": {},
-  "schema": {}, 
+  "services": ["mqtt:want"],
+  "options": {
+    "poll_interval": 30
+  },
+  "schema": {
+    "poll_interval": "int(5,3600)",
+    "mqtt_host": "str?",
+    "mqtt_port": "port?",
+    "mqtt_user": "str?",
+    "mqtt_password": "password?"
+  },
   "arch": ["aarch64"],
   "devices": [ "/dev/i2c-1" ]
-
 }

hassio-addon-lifepo4wered/lifepo4wered_monitor.py

@@ -0,0 +1,285 @@
+#!/usr/bin/env python3
+"""Publish LiFePO4wered/Pi+ UPS stats to MQTT with Home Assistant autodiscovery.
+
+Polls `lifepo4wered-cli get`, publishes the parsed registers as one JSON
+payload, and announces entities via MQTT discovery. Configured entirely
+through environment variables (see main()).
+"""
+
+import json
+import logging
+import os
+import signal
+import subprocess
+import sys
+import time
+
+try:
+    import paho.mqtt.client as mqtt
+except ImportError:  # allow unit-testing parse/discovery without paho
+    mqtt = None
+
+LOG = logging.getLogger("lifepo4wered_monitor")
+
+CLI_COMMAND = ["lifepo4wered-cli", "get"]
+CLI_TIMEOUT = 10
+
+# Sample of real `lifepo4wered-cli get` output; used when LIFEPO4WERED_FAKE=1.
+SAMPLE_OUTPUT = """\
+I2C_REG_VER = 7
+I2C_ADDRESS = 67
+LED_STATE = 1
+TOUCH_STATE = 0
+TOUCH_CAP_CYCLES = 0
+TOUCH_THRESHOLD = 12
+TOUCH_HYSTERESIS = 2
+DCO_RSEL = 14
+DCO_DCOMOD = 149
+VIN = 4709
+VBAT = 3233
+VOUT = 4993
+IOUT = 1355
+VBAT_MIN = 2850
+VBAT_SHDN = 2950
+VBAT_BOOT = 3150
+VOUT_MAX = 3500
+VIN_THRESHOLD = 4498
+IOUT_SHDN_THRESHOLD = 0
+VBAT_OFFSET = 103
+VOUT_OFFSET = 108
+VIN_OFFSET = 99
+IOUT_OFFSET = 0
+AUTO_BOOT = 4
+WAKE_TIME = 0
+SHDN_DELAY = 40
+AUTO_SHDN_TIME = 15
+PI_BOOT_TO = 300
+PI_SHDN_TO = 120
+RTC_TIME = 1784323638
+RTC_WAKE_TIME = 0
+WATCHDOG_CFG = 0
+WATCHDOG_GRACE = 20
+WATCHDOG_TIMER = 20
+PI_RUNNING = 1
+CFG_WRITE = 0
+"""
+
+DEVICE = {
+    "identifiers": ["lifepo4wered_pi"],
+    "name": "LiFePO4wered/Pi+",
+    "manufacturer": "Silicognition LLC",
+    "model": "LiFePO4wered/Pi+",
+}
+
+# (register, entity name) — millivolt registers shown as V main sensors
+MAIN_VOLTAGE = [
+    ("VIN", "Input voltage"),
+    ("VBAT", "Battery voltage"),
+    ("VOUT", "Output voltage"),
+]
+
+# millivolt threshold registers, shown as diagnostic V sensors
+DIAG_VOLTAGE = [
+    ("VBAT_MIN", "Battery minimum voltage"),
+    ("VBAT_SHDN", "Battery shutdown voltage"),
+    ("VBAT_BOOT", "Battery boot voltage"),
+    ("VOUT_MAX", "Output maximum voltage"),
+    ("VIN_THRESHOLD", "Input power threshold"),
+]
+
+# raw-value diagnostic registers (units vary or are unitless flags/timers)
+DIAG_RAW = [
+    ("AUTO_BOOT", "Auto boot mode"),
+    ("SHDN_DELAY", "Shutdown delay"),
+    ("AUTO_SHDN_TIME", "Auto shutdown time"),
+    ("PI_BOOT_TO", "Pi boot timeout"),
+    ("PI_SHDN_TO", "Pi shutdown timeout"),
+    ("WATCHDOG_CFG", "Watchdog mode"),
+    ("WATCHDOG_GRACE", "Watchdog grace"),
+    ("WATCHDOG_TIMER", "Watchdog timer"),
+    ("PI_RUNNING", "Pi running flag"),
+    ("LED_STATE", "LED state"),
+    ("TOUCH_STATE", "Touch state"),
+]
+
+
+def parse_cli_output(text):
+    """Parse `KEY = value` lines into a dict; skip anything malformed."""
+    values = {}
+    for line in text.splitlines():
+        key, sep, value = line.partition("=")
+        if not sep:
+            continue
+        try:
+            values[key.strip()] = int(value.strip())
+        except ValueError:
+            LOG.warning("Skipping malformed line: %r", line)
+    return values
+
+
+def read_values():
+    """Run the CLI (or use the embedded sample) and return parsed registers."""
+    if os.environ.get("LIFEPO4WERED_FAKE"):
+        return parse_cli_output(SAMPLE_OUTPUT)
+    output = subprocess.run(
+        CLI_COMMAND, capture_output=True, text=True,
+        timeout=CLI_TIMEOUT, check=True,
+    ).stdout
+    return parse_cli_output(output)
+
+
+def discovery_messages(discovery_prefix, state_topic, availability_topic):
+    """Yield (topic, config-dict) pairs for every Home Assistant entity."""
+
+    def entity(component, key, name, **extra):
+        cfg = {
+            "name": name,
+            "unique_id": "lifepo4wered_" + key.lower(),
+            "state_topic": state_topic,
+            "availability_topic": availability_topic,
+            "device": DEVICE,
+        }
+        cfg.update(extra)
+        topic = "%s/%s/lifepo4wered/%s/config" % (
+            discovery_prefix, component, key.lower())
+        return topic, cfg
+
+    def millivolts(key):
+        return "{{ (value_json.%s / 1000) | round(3) }}" % key
+
+    for key, name in MAIN_VOLTAGE:
+        yield entity(
+            "sensor", key, name,
+            device_class="voltage",
+            unit_of_measurement="V",
+            state_class="measurement",
+            suggested_display_precision=2,
+            value_template=millivolts(key),
+        )
+
+    yield entity(
+        "sensor", "IOUT", "Output current",
+        device_class="current",
+        unit_of_measurement="A",
+        state_class="measurement",
+        suggested_display_precision=2,
+        value_template="{{ (value_json.IOUT / 1000) | round(3) }}",
+    )
+
+    yield entity(
+        "binary_sensor", "EXTERNAL_POWER", "External power",
+        device_class="power",
+        value_template=(
+            "{{ 'ON' if value_json.VIN >= value_json.VIN_THRESHOLD"
+            " else 'OFF' }}"),
+    )
+
+    for key, name in DIAG_VOLTAGE:
+        yield entity(
+            "sensor", key, name,
+            device_class="voltage",
+            unit_of_measurement="V",
+            entity_category="diagnostic",
+            suggested_display_precision=2,
+            value_template=millivolts(key),
+        )
+
+    for key, name in DIAG_RAW:
+        yield entity(
+            "sensor", key, name,
+            entity_category="diagnostic",
+            value_template="{{ value_json.%s }}" % key,
+        )
+
+    yield entity(
+        "sensor", "RTC_TIME", "UPS clock",
+        device_class="timestamp",
+        entity_category="diagnostic",
+        value_template="{{ value_json.RTC_TIME | as_datetime }}",
+    )
+
+
+def make_client(host, port, username, password, availability_topic):
+    client_kwargs = {"client_id": "lifepo4wered_monitor"}
+    try:
+        client = mqtt.Client(
+            callback_api_version=mqtt.CallbackAPIVersion.VERSION2,
+            **client_kwargs)
+    except AttributeError:  # paho-mqtt 1.x
+        client = mqtt.Client(**client_kwargs)
+    if username:
+        client.username_pw_set(username, password or None)
+    client.will_set(availability_topic, "offline", retain=True)
+    client.connect(host, port, keepalive=60)
+    return client
+
+
+def main():
+    logging.basicConfig(
+        level=os.environ.get("LOG_LEVEL", "INFO").upper(),
+        format="%(asctime)s %(levelname)s %(message)s")
+
+    host = os.environ.get("MQTT_HOST", "localhost")
+    port = int(os.environ.get("MQTT_PORT", "1883"))
+    username = os.environ.get("MQTT_USER", "")
+    password = os.environ.get("MQTT_PASSWORD", "")
+    interval = float(os.environ.get("POLL_INTERVAL", "30"))
+    discovery_prefix = os.environ.get("DISCOVERY_PREFIX", "homeassistant")
+    topic_prefix = os.environ.get("MQTT_TOPIC_PREFIX", "lifepo4wered")
+
+    state_topic = topic_prefix + "/state"
+    availability_topic = topic_prefix + "/availability"
+
+    if mqtt is None:
+        LOG.error("paho-mqtt is not installed")
+        return 1
+
+    def on_connect(client, userdata, flags, reason_code, properties=None):
+        LOG.info("Connected to MQTT broker %s:%d", host, port)
+        for topic, cfg in discovery_messages(
+                discovery_prefix, state_topic, availability_topic):
+            client.publish(topic, json.dumps(cfg), retain=True)
+        client.publish(availability_topic, "online", retain=True)
+
+    client = make_client(host, port, username, password, availability_topic)
+    client.on_connect = on_connect
+    client.loop_start()
+
+    running = True
+
+    def stop(signum, frame):
+        nonlocal running
+        running = False
+
+    signal.signal(signal.SIGTERM, stop)
+    signal.signal(signal.SIGINT, stop)
+
+    online = True
+    while running:
+        try:
+            values = read_values()
+        except (subprocess.SubprocessError, OSError) as exc:
+            LOG.error("Failed to read UPS state: %s", exc)
+            if online:
+                client.publish(availability_topic, "offline", retain=True)
+                online = False
+        else:
+            if not online:
+                client.publish(availability_topic, "online", retain=True)
+                online = True
+            client.publish(state_topic, json.dumps(values), retain=True)
+            LOG.debug("Published %d values", len(values))
+        # sleep in small steps so SIGTERM is handled promptly
+        deadline = time.monotonic() + interval
+        while running and time.monotonic() < deadline:
+            time.sleep(1)
+
+    LOG.info("Shutting down")
+    client.publish(availability_topic, "offline", retain=True)
+    client.loop_stop()
+    client.disconnect()
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

hassio-addon-lifepo4wered/run.sh

@@ -1,3 +1,33 @@
 #!/usr/bin/with-contenv bashio
 
-echo Hello world!
+export POLL_INTERVAL="$(bashio::config 'poll_interval')"
+
+# Manual MQTT settings from addon options win; otherwise use the broker
+# provided by the Supervisor (e.g. the Mosquitto addon).
+if bashio::config.has_value 'mqtt_host'; then
+    export MQTT_HOST="$(bashio::config 'mqtt_host')"
+    if bashio::config.has_value 'mqtt_port'; then
+        export MQTT_PORT="$(bashio::config 'mqtt_port')"
+    fi
+    if bashio::config.has_value 'mqtt_user'; then
+        export MQTT_USER="$(bashio::config 'mqtt_user')"
+    fi
+    if bashio::config.has_value 'mqtt_password'; then
+        export MQTT_PASSWORD="$(bashio::config 'mqtt_password')"
+    fi
+elif bashio::services.available "mqtt"; then
+    export MQTT_HOST="$(bashio::services mqtt 'host')"
+    export MQTT_PORT="$(bashio::services mqtt 'port')"
+    export MQTT_USER="$(bashio::services mqtt 'username')"
+    export MQTT_PASSWORD="$(bashio::services mqtt 'password')"
+else
+    bashio::log.warning \
+        "No MQTT broker configured and no mqtt service available;" \
+        "trying localhost:1883"
+fi
+
+bashio::log.info "Starting lifepo4wered-daemon"
+lifepo4wered-daemon -f &
+
+bashio::log.info "Starting MQTT monitor (poll interval: ${POLL_INTERVAL}s)"
+exec python3 /usr/bin/lifepo4wered_monitor.py

tests/stubs/paho/mqtt/client.py

@@ -0,0 +1,41 @@
+"""Minimal paho-mqtt stand-in for end-to-end smoke tests without a broker.
+
+Every publish is appended to the file named by $STUB_MQTT_LOG as
+"<topic>\t<payload>".
+"""
+
+import os
+
+
+class CallbackAPIVersion:
+    VERSION1 = 1
+    VERSION2 = 2
+
+
+class Client:
+    def __init__(self, *args, **kwargs):
+        self.on_connect = None
+        self._log = open(os.environ["STUB_MQTT_LOG"], "a")
+
+    def username_pw_set(self, username, password=None):
+        pass
+
+    def will_set(self, topic, payload=None, qos=0, retain=False):
+        pass
+
+    def connect(self, host, port=1883, keepalive=60):
+        pass
+
+    def loop_start(self):
+        if self.on_connect:
+            self.on_connect(self, None, {}, 0, None)
+
+    def loop_stop(self):
+        pass
+
+    def disconnect(self):
+        self._log.close()
+
+    def publish(self, topic, payload=None, qos=0, retain=False):
+        self._log.write("%s\t%s\n" % (topic, payload))
+        self._log.flush()

tests/test_monitor.py

@@ -0,0 +1,97 @@
+import json
+import os
+import sys
+import unittest
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..",
+                                "hassio-addon-lifepo4wered"))
+
+import lifepo4wered_monitor as mon
+
+
+class ParseOutputTest(unittest.TestCase):
+    def test_parses_sample_output(self):
+        values = mon.parse_cli_output(mon.SAMPLE_OUTPUT)
+        self.assertEqual(values["VIN"], 4709)
+        self.assertEqual(values["VBAT"], 3233)
+        self.assertEqual(values["IOUT"], 1355)
+        self.assertEqual(values["PI_RUNNING"], 1)
+        self.assertEqual(len(values), 36)
+
+    def test_skips_malformed_lines(self):
+        values = mon.parse_cli_output("VIN = 5000\ngarbage line\nVBAT = abc\n")
+        self.assertEqual(values, {"VIN": 5000})
+
+    def test_handles_negative_values(self):
+        values = mon.parse_cli_output("IOUT_OFFSET = -12\n")
+        self.assertEqual(values["IOUT_OFFSET"], -12)
+
+
+class DiscoveryTest(unittest.TestCase):
+    def setUp(self):
+        self.messages = dict(mon.discovery_messages(
+            discovery_prefix="homeassistant",
+            state_topic="lifepo4wered/state",
+            availability_topic="lifepo4wered/availability",
+        ))
+
+    def test_main_voltage_sensor(self):
+        topic = "homeassistant/sensor/lifepo4wered/vin/config"
+        self.assertIn(topic, self.messages)
+        cfg = self.messages[topic]
+        self.assertEqual(cfg["device_class"], "voltage")
+        self.assertEqual(cfg["unit_of_measurement"], "V")
+        self.assertEqual(cfg["state_class"], "measurement")
+        self.assertIn("value_json.VIN", cfg["value_template"])
+        self.assertNotIn("entity_category", cfg)
+
+    def test_current_sensor(self):
+        cfg = self.messages["homeassistant/sensor/lifepo4wered/iout/config"]
+        self.assertEqual(cfg["device_class"], "current")
+        self.assertEqual(cfg["unit_of_measurement"], "A")
+
+    def test_external_power_binary_sensor(self):
+        topic = "homeassistant/binary_sensor/lifepo4wered/external_power/config"
+        self.assertIn(topic, self.messages)
+        cfg = self.messages[topic]
+        self.assertEqual(cfg["device_class"], "power")
+        self.assertIn("VIN_THRESHOLD", cfg["value_template"])
+
+    def test_diagnostic_entities_are_categorized(self):
+        cfg = self.messages["homeassistant/sensor/lifepo4wered/vbat_shdn/config"]
+        self.assertEqual(cfg["entity_category"], "diagnostic")
+        self.assertEqual(cfg["unit_of_measurement"], "V")
+
+    def test_skipped_registers_have_no_entity(self):
+        for key in ("i2c_reg_ver", "dco_rsel", "vbat_offset", "cfg_write"):
+            self.assertNotIn(
+                "homeassistant/sensor/lifepo4wered/%s/config" % key,
+                self.messages)
+
+    def test_common_fields(self):
+        for topic, cfg in self.messages.items():
+            self.assertEqual(cfg["state_topic"], "lifepo4wered/state")
+            self.assertEqual(cfg["availability_topic"],
+                             "lifepo4wered/availability")
+            self.assertTrue(cfg["unique_id"].startswith("lifepo4wered_"),
+                            topic)
+            self.assertEqual(cfg["device"]["identifiers"], ["lifepo4wered_pi"])
+            json.dumps(cfg)  # must be serializable
+
+    def test_unique_ids_are_unique(self):
+        ids = [cfg["unique_id"] for cfg in self.messages.values()]
+        self.assertEqual(len(ids), len(set(ids)))
+
+
+class ReadValuesTest(unittest.TestCase):
+    def test_fake_mode(self):
+        os.environ["LIFEPO4WERED_FAKE"] = "1"
+        try:
+            values = mon.read_values()
+        finally:
+            del os.environ["LIFEPO4WERED_FAKE"]
+        self.assertEqual(values["VOUT"], 4993)
+
+
+if __name__ == "__main__":
+    unittest.main()