Victron Energy Cerbo GX MK2

Battery and energy-system communications hub

Cerbo GX MK2 brings connected Victron equipment into one local energy-system interface. It is a communications hub, not a power inverter or a calibrated energy meter. A Modbus TCP client selects the system aggregate or an individual connected service using the unit ID, then reads the registers belonging to that service. The available measurements therefore depend on the equipment actually connected.

Victron Energy Cerbo GX MK2
  • Modbus TCP

Battery and energy-system communications hub

Compatibility

Compatible through local Modbus TCP

Victron documents a local Modbus TCP gateway for GX devices. Edge reads its published register map using the unit ID of the required connected service.

Cerbo GX MK2 part numbers BPP900450110 and BPP900451100. The current manual also covers MK3; its higher VE.Direct device limit is not a MK2 specification. This guide reads data only and does not configure ESS control, battery limits or generator operation.

Connect it with

For local measurements from equipment already visible on the GX device

  • Modbus
  • Edge
  • Platforms
Battery and energy-system communications hub
Interface
Gateway
Edge
Output
Cerbo GX MK2Cerbo GX MK2 and connected energy devices
Protected EthernetSegmented LAN
ZGW-20 GatewayHosts Edge locally
EpiSensor EdgeEdge Modbus client
Customer platformMQTT · API · files
Modbus TCP
Protected Ethernet
Runs locally
Optional onward data
Enable the GX Modbus TCP service and record the Available services list. Each connected service has a unit ID. Unit ID 100 selects the overall system service; a battery monitor or VE.Bus inverter/charger requires its own listed ID and corresponding register set. The customer-platform output is optional; Edge remains the local system of record.

Models

Download
ModelsInterfaceRoute into Edge
Cerbo GX MK2, BPP900450110 / BPP9004511008–70 V DC communications hub; Ethernet, VE.Bus, VE.Direct and VE.Can interfacesRead the configured local Modbus gateway and preserve the service-to-unit-ID mapping.
Cerbo GX MK3, BPP900451130Separate hardware revision; the current manual lists up to 25 VE.Direct devices versus 15 for MK2Do not apply MK3 capacity to a MK2 installation.
Original Cerbo GX and Cerbo-S GXEarlier hardware with separate archived manualsMany functions depend on Venus OS, but hardware ports and limits must come from the exact model manual.

Specifications

MK2 is a low-voltage DC-powered hub for connected energy equipment. Its three physical VE.Direct ports can be extended through USB within the documented 15-device total, which includes both direct and USB-connected VE.Direct devices. The measured accuracy belongs to the connected meter, monitor or inverter rather than the hub.12

Exact hardware
Cerbo GX MK2: BPP900450110 or BPP9004511002
Supply
8–70 V DC2
Network
10/100 Ethernet; Wi-Fi available2
VE.Direct capacity
3 physical ports; maximum 15 connected VE.Direct devices in total, including USB2
System unit ID
100 for com.victronenergy.system; connected services use their listed IDs1
Installation envelope
IP20; -20 to +50 °C; wall mounting or optional DIN-rail adapter2

Interface

Documented measurements and integration boundaries for Cerbo GX MK2.

  • System aggregate data from com.victronenergy.system, using unit ID 100.
  • Battery monitor, SmartShunt or supported CAN-battery measurements through the corresponding battery service.
  • VE.Bus inverter/charger AC input and output data, selected by the actual service unit ID.
  • Solar-charger data from connected VE.Direct or VE.Can equipment.
  • Grid-meter and PV-inverter data only when those devices are present and correctly configured on GX.
  • Last Modbus error and device availability to distinguish a missing service from a legitimate zero reading.

Assessment

Cerbo GX MK2 hardware BPP900450110/BPP900451100; read-only Modbus gateway integration with connected equipment.

InteroperabilityWell supported
The public GX protocol documents function codes, per-service unit IDs, the register workbook and a worked read. Available points depend on the connected service.1
AccuracySupported with conditions
System and individual-device services are distinguished. The hub does not supply a measurement-accuracy class; suitability depends on the connected monitor, meter or inverter and its configured role.12
SecuritySupported with conditions
Venus OS documents network security profiles and authenticated console access. Modbus remains a separately enabled read/write service requiring local access restriction.14
ReliabilitySupported with conditions
The 8–70 V DC power range, named EMC/safety standards, persistent unit IDs and stored firmware backup provide documented operating and recovery boundaries. Connected-device failure still produces unavailable readings.125
RuggednessSupported with conditions
IP20 and -20 to +50 °C suit a protected cabinet or indoor installation. An outdoor or wet site needs an appropriate enclosure rather than relying on the hub housing.2
ScalabilitySupported with conditions
The service mapping supports multiple devices behind one IP address. MK2 has an explicit 15-device total for VE.Direct connections; polling must avoid undefined register gaps.12
LifecycleSupported with conditions
Victron documents Venus OS updates, a stored firmware backup and separate manuals for older hardware. Firmware capability and physical hardware capacity remain distinct.35

Setup

Read a connected VE.Bus AC input voltage

Victron’s GX manual provides this example for a Multi or Quattro connected over VE.Bus. It tests service selection and scaling, not the Cerbo’s own supply voltage.

Target
Unit ID 246 in the manufacturer example; use the actual VE.Bus ID shown under Available services
Function
FC03 Read Holding Registers; Victron also supports equivalent FC04 reads
Address and length
PDU address 3, one register; do not subtract one
Request PDU
03 00 03 00 01
Manufacturer example
Raw register 2302, hexadecimal 0x08FE
Independent response/decode fixture
03 02 08 FE gives U16 2302; divide by 10 = 230.2 V AC
Acceptance boundary
A connected VE.Bus service and valid AC input are required. Check the same quantity and phase on the GX screen.

Acceptance: The example demonstrates a valid unit-ID/register pairing and a ×0.1 voltage scale. It does not establish battery data, all system phases or physical-site qualification. Use the current workbook for each additional point.

  1. Confirm MK2 and the measurement source

    Record the GX part number and Venus OS version. Check that the target inverter/charger, battery monitor or meter already appears correctly in the GX device list. A gateway cannot expose measurements from equipment that is absent or not communicating.

  2. Enable the GX Modbus service

    Enable Modbus TCP in the GX settings. The GX Modbus manual documents Settings, Services, Modbus/TCP; menu placement can differ with Venus OS interface versions. Use the service’s Available services list to record unit IDs. Keep the IP endpoint on a protected local network.

  3. Choose system totals or an individual service

    Use unit ID 100 only for the overall system register set. Select the listed VE.Bus, battery, grid-meter or solar-charger unit ID for that service’s registers. Download the official register workbook linked from Victron’s Modbus manual and retain its revision with your configuration.

  4. Perform the bounded voltage read

    For a connected VE.Bus Multi or Quattro, verify its unit ID and read register address 3 as shown below. Compare the decoded AC input voltage with the corresponding GX device screen. Do not compare it with an unrelated phase, AC output or DC battery voltage.

  5. Handle absent data and changes

    Read only defined registers and do not combine blocks across unsupported gaps. Treat missing-device and illegal-address exceptions as unavailable data. Reconfirm the service mapping and available measurements after adding equipment, replacing hardware or updating Venus OS; the manufacturer documents unit IDs as persistent across reboot.

Common questions

Why does unit ID 100 not return my battery-monitor registers?
Unit ID 100 selects the aggregate system service. Individual battery services have separate IDs and register sets. The same IP address can expose many logical devices, so both fields must match.1
Can I read every register in one large block?
Only combine contiguous registers that exist for that service. Victron warns that a request spanning nonexistent registers fails. Available data also varies between battery monitors and CAN-connected batteries.1
Does the GX security profile encrypt Modbus TCP?
The network security profile governs services such as Remote Console access. The documented Modbus TCP path is separate; do not assume an HTTPS login protects its register traffic. Restrict Modbus access on the local network and keep control commands out of the monitoring client.14
Can the Cerbo replace an energy meter?
No. It collects and presents measurements from connected devices and system calculations. Select and verify the underlying meter for the accuracy and electrical boundary required.13

Sources

  1. GX Modbus-TCP manual: unit IDs, registers and worked voltage example (opens in a new tab) Victron Energy
  2. Cerbo GX manual: MK2 and MK3 technical specifications (opens in a new tab) Victron Energy
  3. Cerbo GX manual: product role and discontinued-model documentation (opens in a new tab) Victron Energy
  4. Cerbo GX manual: user interface and network security profiles (opens in a new tab) Victron Energy
  5. Cerbo GX manual: firmware updates and stored firmware backup (opens in a new tab) Victron Energy

Further reading

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