Marstek Venus E Gen 3.0 (battery)
The Marstek Venus E Gen 3.0 is an AC-coupled residential battery storage system with a 5.12 kWh LiFePO4 pack, designed to maximise solar self-consumption alongside an existing grid-tied inverter. This ModbusCloud template reads AC power flow (charge and discharge direction) and battery state of charge via Modbus TCP, and exposes four write registers that control operating mode, force charge/discharge direction, and charge power setpoint. Integrators can monitor live energy balance and push remote mode changes through the ModbusCloud Gateway without relying on the Marstek app.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 7, read and write
- Brand
- Marstek
- Last updated
Registers (7)
3 read, 4 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| power | W | Read | |||
| energy | Wh | Read | |||
| soc | % | Read | |||
| batterymode_a | Write | ||||
| batterymode_b | Write | ||||
| batterymode_e | Write | ||||
| batterymode_h | W | Write |
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Use cases
- Monitor battery state of charge in real time to verify the system charges fully during peak solar hours.
- Track the power register to confirm the battery is discharging into the home during evening demand peaks.
- Alert on sustained zero power readings after a forced charge command to detect communication or RS485 control-mode failures.
- Compare cumulative energy throughput over time to estimate battery cycle consumption across multiple sites.
- Verify work-mode setpoint register after a remote change to confirm anti-feed or trade mode is active as intended.
Installation
Connect the Marstek Venus E Gen 3.0 RS485 port to an RS485-to-TCP bridge (such as a PUSR DR-134 or Elfin EW11) and ensure the bridge is on the same LAN as the ModbusCloud Gateway; note that swapped A/B wires are the most common wiring fault.
In the ModbusCloud portal, add your ModbusCloud Gateway, then import the Marstek Venus E Gen 3.0 template and assign the correct Modbus unit ID (slave ID) matching the bridge configuration, typically 1.
Before writing any control registers, send value 0x55AA (21930 decimal) to the RS485 control-mode register (42000) to unlock the 42000 to 42999 register range; without this step all write commands will be rejected.
Spot-check the installation by reading the soc register (34002) in the portal live-data view and confirming the value matches the percentage shown on the Marstek app or front panel.
Things to watch for
All write commands fail. What is the most likely cause?
The battery must be in RS485 control mode before any holding register in the 42000 to 42999 range accepts writes. Write 0x55AA (decimal 21930) to register 42000 first. Some firmware versions time out the control mode and require a keep-alive write to 42000 every 25 seconds or less. ModbusCloud writes registers at most once per minute, so on those firmware versions controlling the battery through ModbusCloud is not possible, while reading its values works.
No values appear even though the gateway is connected. What now?
Check A/B polarity on the RS485 cable. The Marstek Venus E Gen 3.0 RS485 wiring is a common source of reversed connections. Swapping the two data wires immediately resolves 'no response' errors. Also confirm the RS485-to-TCP bridge is configured for port 502 and the correct baud rate (typically 9600).
The soc or power register returns a constant wrong value after a firmware update.
Register addresses changed between Generation 2 and Gen 3.0 firmware versions and may shift again after updates. The Gen 3.0 addresses in this template (30006, 33002, 34002) are specific to that hardware revision. If values look wrong after a firmware update, verify the firmware version and cross-check register addresses in the Marstek Modbus documentation for that version.
Is it safe to write force charge or work-mode registers continuously?
Use write registers with care. Holding the battery in forced charge or discharge mode at maximum power outside its design limits may trigger BMS protection trips or affect long-term cell health. Always verify the power setpoint is within the device's rated range, test mode changes during off-peak periods first, and confirm your local utility regulations permit remote control.
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