Batt Monitoring Modbus Register 3: Battery2 SOC

Technical Definition

The register Battery2 SOC at address 3 is used to monitor battery2 soc on the Batt Monitoring.

• Protocol: Modbus RTU
• Data Type: U WORD
• Unit: %
• Access: Read Only

How to Read (Python pymodbus)

Use this code snippet to read this specific value via RS485:

from pymodbus.client.sync import ModbusSerialClient

client = ModbusSerialClient(method='rtu', port='/dev/ttyUSB0', baudrate=9600)
client.connect()

# Read Battery2_SOC (Address: 3)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=3, count=2, unit=1)

if not result.isError():
    print(f"Raw Value: {result.registers}")
else:
    print("Error reading register")

client.close()

Integration (Home Assistant)

Paste this into your configuration.yaml:

- platform: modbus_controller
  name: "Battery2_SOC"
  address: 3
  value_type: U_WORD
  unit_of_measurement: "%"

Connection Diagram

Here is the standard RS485 wiring for this configuration:

graph TD
    PLC[Host Controller / Home Assistant]
    Device[Batt Monitoring]

    PLC -- "A+ (D+)" --> Device
    PLC -- "B- (D-)" --> Device
    PLC -- GND --> Device

💡 Engineer's Insight

Analysis: Battery 2 State of Charge (SOC), expressed as a percentage (%). Indicates the remaining capacity of the battery.

Troubleshooting: Consistently zero or low SOC could point to a calibration issue, faulty battery, or BMS communication error. Erratic readings suggest sensor problems.