All registers return zero or no data. What is wrong?

The FEMS Modbus/TCP interface is disabled by default. You must install and activate the FEMS App Modbus/TCP Read Access in the FEMS App Center. Without this app, the FEMS will not respond on port 502, even if the device is reachable on the network.

Register addresses appear shifted by one. Why?

Some Modbus client tools default to a base address of 1 rather than 0. The register addresses in this template are 0-indexed. Set your client base address to 0, or in QModMaster change the Base Address field to 0, otherwise every address will be off by one.

I wrote to grid_max_charge_current_a but nothing changed. What now?

Write registers require the FEMS App Modbus/TCP Write Access (a separate, paid app). Read access does not grant write permissions. Also confirm the Watchdog timeout: write commands expire after 60 seconds by default, so repeated writes are needed for sustained setpoints. Never exceed hardware-rated current limits when writing charge or discharge current setpoints, as this can trigger protection shutdowns.

The gateway connects but BECU cell section registers read garbage values.

Cell section registers (addresses 3020 to 3051 for voltage, 3036 to 3051 for temperature) carry raw unitless values. Verify the scaling documented in your system's Modbus table, which you can download as an Excel file from the FEMS Online Monitoring under the system profile. If the FEMS firmware is outdated, some cell section registers may not be populated; check for pending over-the-air updates.

Free Modbus template: Fenecon Mini Ess

Name: Fenecon Mini Ess
Brand: Fenecon
SKU: ca64586d-b055-4f9b-a195-2260f3ef8567

The Fenecon Mini Ess is a compact residential and light-commercial battery energy storage system managed by the FENECON FEMS energy management platform. This ModbusCloud template communicates over Modbus TCP and exposes a comprehensive register set covering system state, control mode, and grid mode, as well as per-phase AC active power on L1, L2, and L3. Battery-side data includes pack voltage, current, power, and system-level state of charge, plus granular per-cell voltage and temperature sections from two independent BECU units. Write registers allow configuration of grid charge and discharge current limits, PCS mode, setup mode, and RTC synchronisation. Connecting the Fenecon Mini Ess to your ModbusCloud portal gives installers deep visibility into battery health and charge behaviour across the full cell array.

Registers (97)

86 read / 11 write

Name	Address	Function	Type	Unit	Access
system_state Overall ESS system state enumeration (standby, start, fault, etc.).	100	FC03	uint16		R
control_mode Active control mode of the ESS (remote, local, or scheduled).	101	FC03	uint16		R
battery_group_state Operational state of the battery group (idle, charge, discharge, fault).	108	FC03	uint16		R
battery_voltage DC battery pack total voltage in volts.	110	FC03	uint16	V	R
battery_current DC battery current in amperes, positive for charge, negative for discharge.	111	FC03	int16	A	R
battery_power DC battery power in watts, positive for charge, negative for discharge.	112	FC03	int16	W	R
active_power_l1 AC active power on phase L1 in watts.	2007	FC03	uint16	W	R
active_power_l2 AC active power on phase L2 in watts.	2107	FC03	uint16	W	R
active_power_l3 AC active power on phase L3 in watts.	2207	FC03	uint16	W	R
becu1_allowed_charge_current BECU1 maximum allowed charge current in amperes.	3000	FC03	uint16	A	R
becu1_allowed_discharge_current BECU1 maximum allowed discharge current in amperes.	3001	FC03	uint16	A	R
becu1_total_voltage BECU1 total battery string voltage in volts.	3002	FC03	uint16	V	R
becu1_total_current BECU1 total battery string current in amperes.	3003	FC03	uint16	A	R
becu1_soc BECU1 battery unit state of charge, 0 to 100 percent.	3004	FC03	uint16	%	R
becu1_version BECU1 battery management unit firmware version number.	3009	FC03	uint16		R
becu1_nominal_capacity BECU1 rated (nominal) energy capacity value.	3010	FC03	uint16		R
becu1_current_capacity BECU1 present usable capacity, reflecting degradation.	3011	FC03	uint16		R
becu1_minimum_voltage_no Cell index number of the lowest-voltage cell in BECU1.	3012	FC03	uint16		R
becu1_minimum_voltage Lowest individual cell voltage in BECU1, in volts.	3013	FC03	uint16	V	R
becu1_maximum_voltage_no Cell index number of the highest-voltage cell in BECU1.	3014	FC03	uint16		R
becu1_maximum_voltage Highest individual cell voltage in BECU1, in volts.	3015	FC03	uint16	V	R
becu1_minimum_temperature_no Sensor index of the coldest temperature sensor in BECU1.	3016	FC03	uint16		R
becu1_minimum_temperature Lowest cell temperature in BECU1, degrees Celsius.	3017	FC03	uint16	°C	R
becu1_maximum_temperature_no Sensor index of the hottest temperature sensor in BECU1.	3018	FC03	uint16		R
becu1_maximum_temperature Highest cell temperature in BECU1, degrees Celsius.	3019	FC03	uint16	°C	R
battery_voltage_section_1 Raw voltage reading for battery cell section 1.	3020	FC03	uint16		R
battery_voltage_section_2 Raw voltage reading for battery cell section 2.	3021	FC03	uint16		R
battery_voltage_section_3 Raw voltage reading for battery cell section 3.	3022	FC03	uint16		R
battery_voltage_section_4 Raw voltage reading for battery cell section 4.	3023	FC03	uint16		R
battery_voltage_section_5 Raw voltage reading for battery cell section 5.	3024	FC03	uint16		R
battery_voltage_section_6 Raw voltage reading for battery cell section 6.	3025	FC03	uint16		R
battery_voltage_section_7 Raw voltage reading for battery cell section 7.	3026	FC03	uint16		R
battery_voltage_section_8 Raw voltage reading for battery cell section 8.	3027	FC03	uint16		R
battery_voltage_section_9 Raw voltage reading for battery cell section 9.	3028	FC03	uint16		R
battery_voltage_section_10 Raw voltage reading for battery cell section 10.	3029	FC03	uint16		R
battery_voltage_section_11 Raw voltage reading for battery cell section 11.	3030	FC03	uint16		R
battery_voltage_section_12 Raw voltage reading for battery cell section 12.	3031	FC03	uint16		R
battery_voltage_section_13 Raw voltage reading for battery cell section 13.	3032	FC03	uint16		R
battery_voltage_section_14 Raw voltage reading for battery cell section 14.	3033	FC03	uint16		R
battery_voltage_section_15 Raw voltage reading for battery cell section 15.	3034	FC03	uint16		R
battery_voltage_section_16 Raw voltage reading for battery cell section 16.	3035	FC03	uint16		R
battery_temperature_section_1 Raw temperature reading for battery cell section 1.	3036	FC03	uint16		R
battery_temperature_section_2 Raw temperature reading for battery cell section 2.	3037	FC03	uint16		R
battery_temperature_section_3 Raw temperature reading for battery cell section 3.	3038	FC03	uint16		R
battery_temperature_section_4 Raw temperature reading for battery cell section 4.	3039	FC03	uint16		R
battery_temperature_section_5 Raw temperature reading for battery cell section 5.	3040	FC03	uint16		R
battery_temperature_section_6 Raw temperature reading for battery cell section 6.	3041	FC03	uint16		R
battery_temperature_section_7 Raw temperature reading for battery cell section 7.	3042	FC03	uint16		R
battery_temperature_section_8 Raw temperature reading for battery cell section 8.	3043	FC03	uint16		R
battery_temperature_section_9 Raw temperature reading for battery cell section 9.	3044	FC03	uint16		R
battery_temperature_section_10 Raw temperature reading for battery cell section 10.	3045	FC03	uint16		R
battery_temperature_section_11 Raw temperature reading for battery cell section 11.	3046	FC03	uint16		R
battery_temperature_section_12 Raw temperature reading for battery cell section 12.	3047	FC03	uint16		R
battery_temperature_section_13 Raw temperature reading for battery cell section 13.	3048	FC03	uint16		R
battery_temperature_section_14 Raw temperature reading for battery cell section 14.	3049	FC03	uint16		R
battery_temperature_section_15 Raw temperature reading for battery cell section 15.	3050	FC03	uint16		R
battery_temperature_section_16 Raw temperature reading for battery cell section 16.	3051	FC03	uint16		R
becu2_charge_current BECU2 maximum allowed charge current in amperes.	3200	FC03	uint16	A	R
becu2_discharge_current BECU2 maximum allowed discharge current in amperes.	3201	FC03	uint16	A	R
becu2_volt BECU2 total battery string voltage (raw register, no unit scaling).	3202	FC03	uint16		R
becu2_current BECU2 total battery string current in amperes.	3203	FC03	uint16	A	R
becu2_soc BECU2 battery unit state of charge, 0 to 100 percent.	3204	FC03	uint16	%	R
becu2_version BECU2 battery management unit firmware version number.	3209	FC03	uint16		R
becu2_min_volt_no Cell index number of the lowest-voltage cell in BECU2.	3212	FC03	uint16		R
becu2_min_volt Lowest individual cell voltage in BECU2 (raw, no unit).	3213	FC03	uint16		R
becu2_max_volt_no Cell index number of the highest-voltage cell in BECU2.	3214	FC03	uint16		R
becu2_max_volt Highest individual cell voltage in BECU2 (raw, no unit).	3215	FC03	uint16		R
becu2_min_temp_no Sensor index of the coldest temperature sensor in BECU2.	3216	FC03	uint16		R
becu2_min_temp Lowest cell temperature in BECU2 (raw, no unit).	3217	FC03	uint16		R
becu2_max_temp_no Sensor index of the hottest temperature sensor in BECU2.	3218	FC03	uint16		R
becu2_max_temp Highest cell temperature in BECU2 (raw, no unit).	3219	FC03	uint16		R
system_work_state 32-bit system work state bitmask, encodes operational sub-states.	4000	FC03	uint32		R
system_work_mode_state 32-bit system work mode state, encodes current operating mode.	4002	FC03	uint32		R
becu_num Number of active battery energy control units in the system.	4800	FC03	uint16		R
becu_work_state Aggregated BECU operational work state enumeration.	4801	FC03	uint16		R
becu_charge_current Aggregated maximum allowed charge current across all BECUs, amperes.	4803	FC03	uint16	A	R
becu_discharge_current Aggregated maximum allowed discharge current across all BECUs, amperes.	4804	FC03	uint16	A	R
becu_volt Aggregated BECU total voltage (raw register, no unit).	4805	FC03	uint16		R
becu_current Aggregated BECU total current in amperes.	4806	FC03	uint16	A	R
soc System-level battery state of charge, 0 to 100 percent.	4812	FC03	uint16	%	R
rtc_year RTC year setpoint: write to synchronise the system clock.	9014	FC16	uint16		W
rtc_month RTC month setpoint: write to synchronise the system clock.	9015	FC16	uint16		W
rtc_day RTC day setpoint: write to synchronise the system clock.	9016	FC16	uint16		W
rtc_hour RTC hour setpoint: write to synchronise the system clock.	9017	FC16	uint16		W
rtc_minute RTC minute setpoint: write to synchronise the system clock.	9018	FC16	uint16		W
rtc_second RTC second setpoint: write to synchronise the system clock.	9019	FC16	uint16		W
grid_max_charge_current_a Setpoint for maximum grid-side charge current, amperes (write channel A).	30526	FC16	uint16	A	W
grid_max_discharge_current_a Setpoint for maximum grid-side discharge current, amperes (write channel A).	30527	FC16	uint16	A	W
setup_mode_a Setup mode selection setpoint (write channel A).	30558	FC16	uint16		W
pcs_mode_a Power conversion system operating mode setpoint (write channel A).	30559	FC16	uint16		W
grid_max_charge_current_b Readback of the configured maximum grid-side charge current, amperes (read channel B).	30126	FC03	uint16	A	R
grid_max_discharge_current_b Readback of the configured maximum grid-side discharge current, amperes (read channel B).	30127	FC03	uint16	A	R
setup_mode_b Readback of the active setup mode value (read channel B).	30157	FC03	uint16		R
pcs_mode_b Readback of the active PCS operating mode value (read channel B).	30158	FC03	uint16		R
grid_mode Current grid connection mode (on-grid, off-grid, or islanded).	30166	FC03	uint16		R
debug_run_state_a Debug run state register, read access for diagnostics.	2992	FC03	uint16		R
debug_run_state_b Debug run state register, write access for diagnostics.	2992	FC16	uint16		W