All register values show zero or are missing. What is wrong?

The FEMS App Modbus/TCP Read Access must be installed and licensed in the FENECON App Center. Without the app active, the FEMS box does not expose a Modbus TCP server. Confirm the app status in the FEMS live view before troubleshooting the network.

Register addresses seem shifted by one compared to the datasheet. Why?

The FEMS Modbus implementation uses zero-based addressing. Some Modbus tools default to a base address of 1, which shifts every register by one position. Set the base address to 0 in your Modbus client or in the ModbusCloud Gateway configuration to align with the addresses in this template.

The heartbeat write register stops refreshing and the BMS loses control. What now?

The FEMS write watchdog has a default timeout of 60 seconds. Any write command, including the heart_beat_b register, must be refreshed before that window expires. Write the heartbeat at half the timeout interval (every 30 seconds) to maintain a continuous connection. If the watchdog fires, the BMS reverts to autonomous control.

Is it safe to write unit_id or baudrate registers during normal operation?

Writing unit_id or baudrate while the system is in active charge or discharge can disrupt the Modbus session and cause the BMS to lose communication with the inverter, potentially triggering a protection shutdown. Only write these configuration registers during a scheduled maintenance window with the system in standby, and confirm the new settings before resuming operation.

Free Modbus template: Fenecon Commercial

Name: Fenecon Commercial
Brand: Fenecon
SKU: 154b9f43-1742-4b86-90de-35cf04811768

The Fenecon Commercial is a modular, commercial-scale lithium iron phosphate battery energy storage system built around the FENECON Energy Management System (FEMS). It supports multi-tower configurations and communicates via Modbus TCP through the FEMS box. This template reads BMS identity, pack voltage and current, state of charge and health, per-tower SOC, individual cell voltages and temperatures, insulation resistance, cumulative charge and discharge energy, relay status, and available power limits. Write registers allow heartbeat refresh, unit ID assignment, and baud rate configuration. The result is complete battery health visibility for commercial sites inside your ModbusCloud portal.

Registers (56)

51 read / 5 write

Name	Address	Function	Type	Unit	Access
master_mcu_hardware_version Hardware version string of the master MCU board.	0	FC03	string		R
master_mcu_firmware_version Firmware version string of the master MCU.	5	FC03	string		R
slave_mcu_hardware_version Hardware version string of the slave MCU board.	2176	FC03	string		R
slave_mcu_firmware_version Firmware version string of the slave MCU.	2181	FC03	string		R
master_serial_number Serial number string of the master BMS unit.	2762	FC03	string		R
submaster_map_a Bitmask indicating which submaster modules are present, read.	20	FC03	uint32		R
online_tower Bitmask of battery towers currently online.	2628	FC03	uint32		R
running_tower Bitmask of battery towers currently running and active.	2630	FC03	uint32		R
voltage Total DC pack voltage of the battery system, volts.	2680	FC03	int32	V	R
current DC current flowing through the battery pack, amperes.	2682	FC03	int32	A	R
battery_soc Battery state of charge, 0 to 100 percent.	2684	FC03	uint16	%	R
soh Battery state of health, 0 to 100 percent.	2685	FC03	uint16	%	R
nominal_capacity Nominal capacity of the battery system as configured.	2686	FC03	int32	Wh	R
total_charge_capacity_ampere_hours Cumulative total charge delivered to the battery, ampere-hours.	2688	FC03	int64		R
total_discharge_capacity_ampere_hours Cumulative total energy drawn from the battery, ampere-hours.	2692	FC03	int64		R
max_soc Highest state of charge across all towers, percent.	2696	FC03	uint16	%	R
max_soc_tower_id Tower ID reporting the highest state of charge.	2697	FC03	uint16		R
min_soc Lowest state of charge across all towers, percent.	2698	FC03	uint16	%	R
min_soc_tower_id Tower ID reporting the lowest state of charge.	2699	FC03	uint16		R
max_cell_voltage Highest individual cell voltage in the system, millivolts.	2700	FC03	uint16	mV	R
min_cell_voltage Lowest individual cell voltage in the system, millivolts.	2702	FC03	uint16	mV	R
max_cell_temperature Highest cell temperature in the system, degrees Celsius.	2704	FC03	int16	°C	R
min_cell_temperature Lowest cell temperature in the system, degrees Celsius.	2706	FC03	int16	°C	R
insulation_resistance_at_positive_pole Insulation resistance measured at the positive DC pole.	2708	FC03	int32	Ω	R
insulation_resistance_at_negative_pole Insulation resistance measured at the negative DC pole.	2710	FC03	int32	Ω	R
total_charge_capacity_watt_hours Cumulative total charge energy into the battery, watt-hours.	2720	FC03	int64	Wh	R
total_discharge_capacity_watt_hours Cumulative total discharge energy from the battery, watt-hours.	2724	FC03	int64	Wh	R
system_fault_counters Count of recorded system faults since last reset.	2728	FC03	uint16	count	R
insulation_resistance_detection_status Status word for the insulation resistance detection process.	2738	FC03	uint32		R
relay_status Bitmask showing the current state of all BMS relays.	2740	FC03	uint32		R
battery_max_cell_volt Maximum cell voltage threshold used by the BMS.	2742	FC03	uint32	mV	R
battery_min_cell_volt Minimum cell voltage threshold used by the BMS.	2744	FC03	uint32	mV	R
battery_nominal_power Rated nominal power of the battery system, watts.	2774	FC03	uint32	W	R
battery_available_power Instantaneous available power the battery can deliver, watts.	2776	FC03	uint32	W	R
start_charge_voltage_limit Voltage threshold below which charging is permitted to start.	2786	FC03	uint16	mV	R
start_discharge_voltage_limit Voltage threshold above which discharging is permitted to start.	2787	FC03	uint16	mV	R
bp_charge_bms BMS-reported charge power setpoint or limit.	2790	FC03	int32	W	R
bp_discharge_bms BMS-reported discharge power setpoint or limit.	2792	FC03	int32	W	R
charge_max_power Maximum allowable charge power at present conditions, watts.	2794	FC03	int32	W	R
discharge_max_power Maximum allowable discharge power at present conditions, watts.	2796	FC03	int32	W	R
battery_nominal_current Rated nominal current of the battery system, amperes.	2798	FC03	int32	A	R
battery_available_current Instantaneous current the battery can supply or absorb, amperes.	2800	FC03	int32	A	R
soc_for_inverter State of charge value reported to the connected inverter.	2802	FC03	uint16	%	R
charge_max_voltage Maximum charge voltage limit communicated by the BMS, volts.	2804	FC03	uint16	V	R
discharge_min_voltage Minimum discharge cutoff voltage communicated by the BMS, volts.	2805	FC03	uint16	V	R
force_to_charge Flag indicating the BMS is forcing a charge cycle.	2813	FC03	uint16		R
charge_ready Flag indicating the battery is ready to accept charge.	2814	FC03	uint16		R
discharge_ready Flag indicating the battery is ready to supply power.	2815	FC03	uint16		R
heart_beat_a Heartbeat counter read from the BMS, increments each cycle.	3064	FC03	uint32		R
number_of_modules_per_tower Number of battery modules installed in each tower.	3098	FC03	uint16	count	R
number_of_cells_per_module Number of individual cells in each battery module.	3099	FC03	uint16	count	R
unit_id Modbus unit ID setpoint for this BMS device.	17	FC16	uint16		W
unit_number Unit number assignment register for multi-unit configurations.	18	FC16	uint16		W
submaster_map_b Bitmask write register to configure active submaster modules.	20	FC16	uint32		W
baudrate Serial baud rate configuration register for BMS communication.	161	FC16	uint16		W
heart_beat_b Heartbeat write register; must be refreshed to keep watchdog active.	3064	FC16	uint32		W