A battery monitor is switched on but gives no reading

A battery monitor is configured (BATT_MONITOR, or BATT2_MONITOR for battery 2, is not 0) but ArduPilot has no valid reading from it. Either the driver started at power-on is not the type the parameter now asks for, or the sensor reports nothing: an analog pin that is not an analog input, a digital sensor that does not answer, ESC telemetry that carries no voltage.

What to do, most likely first

1. BATT_MONITOR was changed and the flight controller has not been rebooted since.

   CheckIt appears right after you set the monitor type, whatever the type.

   FixReboot. A monitor's driver is created at power-on only; until then the old one, or none, is running.

2. An analog sensor's pins, BATT_VOLT_PIN and BATT_CURR_PIN, are wrong for this board.

   Check-1, or a pin that is not an analog input of this board, makes the monitor unhealthy. With type 3 (voltage only) just the voltage pin counts.

   FixSet the pins the board's documentation gives for its power input and reboot. Loading the board's own firmware on a fresh board sets them by default.

3. The type is a digital sensor (I2C or SMBus, INA2xx, DroneCAN) and the sensor does not answer.

   CheckIs it powered, and on the bus the driver expects? A DroneCAN battery must show up among the CAN nodes in the ground station.

   FixFix the wiring or the bus settings. If no such sensor is fitted, choose the type that matches your power module (4 for the usual analog voltage and current) and reboot.

4. BATT_MONITOR is 9 (ESC) and no ESC is sending its voltage.

   CheckThe ESC voltage in the ground station's status values stays at zero.

   FixGet the ESC telemetry working first: the ESCs' telemetry wire on a serial port, or bidirectional DShot with extended telemetry. Or use the board's own sensor.

5. The words are “feature BATTERY_SUM not available”: type 10 (sum of other monitors) is not built into this board's firmware.

   FixUse another type, or build a firmware with the feature; boards with 1 MB of flash leave it out.

In 4.7 an analog monitor on a board with no free analog input stops the start-up instead, with “Config Error: No analog voltage channel for battery”.

Parameters to look at

Where to do it:Setup & Tuning GuideBoard & Wiring PlannerFirmware Inspector