Battery Modbus Register 74: Total Battery Discharge

Technical Definition

The register Total Battery Discharge at address 74 is used to monitor total battery discharge on the Battery.

• Protocol: Modbus RTU
• Data Type: U DWORD R
• Unit: kWh
• 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 Total Battery Discharge (Address: 74)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=74, 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: "Total Battery Discharge"
  address: 74
  value_type: U_DWORD_R
  unit_of_measurement: "kWh"

Connection Diagram

Here is the standard RS485 wiring for this configuration:

graph TD
    PLC[Host Controller / Home Assistant]
    Device[Battery]

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

💡 Engineer's Insight

Analysis: Total accumulated energy discharged from the battery since its last reset. Units: Watt-hours (Wh) or Kilowatt-hours (kWh).

Troubleshooting: Zero indicates no discharge has occurred or the register was reset. Check battery usage and system configuration.