Battery voltage reads ten times too high. What is wrong?

Register 840 (dc_battery_voltage) uses a scale factor of 10 in the official Victron register list. If your integration applies raw uint16 values without dividing by 10, the voltage will appear ten times larger than the actual DC bus voltage. Divide the raw register value by 10 to obtain volts.

Grid power registers return large positive numbers instead of negative feed-in. Why?

Registers 820 to 822 are signed int16 types. Many Modbus clients default to reading registers as unsigned 16-bit integers. A negative value such as -500 W is encoded as 65036 when treated as unsigned. Configure your client to interpret these registers as signed 16-bit integers to read feed-in power correctly.

The Gateway connects but all registers return zero or unavailable. What now?

Modbus TCP is disabled by default on Victron GX devices. Confirm it is enabled under Settings, then Services, then Modbus TCP on the GX device. Also verify you are polling Unit ID 100. Unit ID 0 maps to the same service but many clients reject it; use 100 as recommended by Victron.

Is it safe to write to the ESS setpoint and limit registers from the portal?

The ESS control registers (addresses 2700 to 2710) are read-only in this template, but treat any external ESS setpoint writes with care. ESS Mode 2 has no automatic passthrough fallback if a controlling script stops updating values, meaning the inverter can continue acting on the last written setpoint until manually overridden. Always test setpoint changes in a controlled environment first.

Free Modbus template: Victron Battery-Inverter

Name: Victron Battery-Inverter
Brand: Victron
SKU: 6644be5c-3585-4d2d-addc-7b44e915ced5

The Victron Battery-Inverter template targets Victron Energy ESS systems monitored through a GX device (Cerbo GX or Venus GX) running Modbus TCP. The template reads the full system picture exposed by the com.victronenergy.system service: per-phase AC consumption, grid power, AC- and DC-coupled PV production, battery state of charge, voltage, current, time-to-go, and VE.Bus charger output. ESS Mode 2 control registers covering the grid setpoint, charge and discharge current limits, max feed-in power, and the PV power limiter flag are also captured. This gives installers a single, structured data source for energy-flow visibility across the entire Victron installation.

Registers (43)

43 read / 0 write

Name	Address	Function	Type	Unit	Access
serial_number System serial number string, identifies the GX device.	800	FC03	string		R
ccgx_relay1_state State of CCGX programmable relay 1, 0 open, 1 closed.	806	FC03	uint16		R
ccgx_relay2_state State of CCGX programmable relay 2, 0 open, 1 closed.	807	FC03	uint16		R
ac_pv_on_output_power_l1 AC-coupled PV power on inverter AC output, phase L1, watts.	808	FC03	uint16	W	R
ac_pv_on_output_power_l2 AC-coupled PV power on inverter AC output, phase L2, watts.	809	FC03	uint16	W	R
ac_pv_on_output_power_l3 AC-coupled PV power on inverter AC output, phase L3, watts.	810	FC03	uint16	W	R
ac_pv_on_input_power_l1 AC-coupled PV power on AC input (grid side), phase L1, watts.	811	FC03	uint16	W	R
ac_pv_on_input_power_l2 AC-coupled PV power on AC input (grid side), phase L2, watts.	812	FC03	uint16	W	R
ac_pv_on_input_power_l3 AC-coupled PV power on AC input (grid side), phase L3, watts.	813	FC03	uint16	W	R
ac_consumption_power_l1 Total AC load consumption on phase L1, watts.	817	FC03	uint16	W	R
ac_consumption_power_l2 Total AC load consumption on phase L2, watts.	818	FC03	uint16	W	R
ac_consumption_power_l3 Total AC load consumption on phase L3, watts.	819	FC03	uint16	W	R
grid_power_l1 Grid power on phase L1, signed, positive import, negative export.	820	FC03	int16	W	R
grid_power_l2 Grid power on phase L2, signed, positive import, negative export.	821	FC03	int16	W	R
grid_power_l3 Grid power on phase L3, signed, positive import, negative export.	822	FC03	int16	W	R
ac_genset_power_l1 Generator AC power contribution on phase L1, signed, watts.	823	FC03	int16	W	R
ac_genset_power_l2 Generator AC power contribution on phase L2, signed, watts.	824	FC03	int16	W	R
ac_genset_power_l3 Generator AC power contribution on phase L3, signed, watts.	825	FC03	int16	W	R
active_input_source Currently active AC input source: 0 not available, 1 grid, 2 generator.	826	FC03	uint16		R
dc_battery_voltage DC battery bus voltage, scaled by 10, volts.	840	FC03	uint16	V	R
dc_battery_current DC battery current, signed, positive charging, negative discharging, amperes.	841	FC03	int16	A	R
active_power Net DC battery power, signed, positive charging, negative discharging, watts.	842	FC03	int16	W	R
battery_soc Battery state of charge, 0 to 100 percent.	843	FC03	uint16	%	R
battery_state Battery operational state code: idle, charging, discharging, or fault.	844	FC03	uint16		R
battery_consumed_amphours Cumulative amp-hours consumed from battery since last reset.	845	FC03	uint16		R
battery_time_to_go Estimated remaining battery runtime at current load, seconds.	846	FC03	uint16	s	R
dc_pv_power Total DC-coupled PV charger output power, watts.	850	FC03	uint16	W	R
dc_pv_current Total DC-coupled PV charger output current, signed, amperes.	851	FC03	int16	A	R
charger_power Total DC charger power delivered to the battery, watts.	855	FC03	uint16	W	R
dc_system_power Net DC system power from non-battery, non-PV DC loads, signed, watts.	860	FC03	int16	W	R
ve_bus_charge_current Charge current delivered by the VE.Bus inverter-charger, signed, amperes.	865	FC03	int16	A	R
ve_bus_charge_power Charge power delivered by the VE.Bus inverter-charger, signed, watts.	866	FC03	int16	W	R
ess_control_loop_setpoint ESS Mode 2 grid power setpoint, positive import, negative export, watts.	2700	FC03	int16	W	R
ess_max_charge_current_percentage ESS Mode 2 maximum charge current limit as percentage of maximum.	2701	FC03	uint16	%	R
ess_max_discharge_current_percentage ESS Mode 2 maximum discharge current limit as percentage of maximum.	2702	FC03	uint16	%	R
ess_control_loop_setpoint_scale_factor_2 ESS control-loop setpoint with 0.01 W scale factor for extended range.	2703	FC03	int16	W	R
ess_max_discharge_power ESS Mode 2 maximum allowed battery discharge power, watts.	2704	FC03	uint16	W	R
system_max_charge_current DVCC system-level maximum charge current limit, amperes.	2705	FC03	int16	A	R
max_feed_in_power Maximum power allowed to feed into the grid, -1 means no limit, watts.	2706	FC03	int16	W	R
feed_excess_dc Flag: 1 permits excess DC-tied PV power to be fed into the grid.	2707	FC03	int16		R
dont_feed_excess_ac Flag: 1 prevents excess AC-tied PV power from being fed into the grid.	2708	FC03	int16		R
pv_power_limiter_active Flag indicating the PV power limiter is currently active, 1 active.	2709	FC03	int16		R
max_charge_voltage Maximum DC charge voltage limit applied to the battery, volts.	2710	FC03	uint16	V	R