The gateway connects but all register values read as zero or timeout.

The Energy Butler GEN3 exposes Modbus over its built-in Wi-Fi or LAN interface using RTU framing encapsulated in TCP. Confirm you are using RTU-over-TCP framing, not plain Modbus TCP. Also verify the slave ID is set to 252 and the correct port (5743 for firmware below V27.52.4.0, or 502 for V27.52.4.0 and above).

Why does the power register at address 30258 show unexpected large values?

Address 30258 is a GEN3 input register range (30000s), decoded as a signed int32 across two consecutive 16-bit registers. Ensure your Modbus client reads two registers starting at 30258 and decodes them as a single int32. A mismatch in register count or byte order will produce garbage values. Positive values indicate discharge; negative values indicate charge.

The soc register reads a value that looks like a raw integer, not a percentage.

Register 33000 returns a uint16. Community integrations have reported that M-TEC applies a scaling factor of 0.01 on the SOC raw value in some firmware versions, producing a raw value of e.g. 9000 for 90%. Verify against the local display and apply the appropriate scale in your portal channel configuration if the raw value is out of the expected 0-100 range.

Is it safe to write to the batterymode register during normal operation?

Use caution when writing to register 50000 (batterymode). Sending an unsupported mode value or switching modes too rapidly can cause the inverter to trip protective limits or enter an unexpected operating state. Always verify the valid mode values in the M-TEC documentation for your firmware version before enabling automated writes, and test manually first.

Free Modbus template: M-TEC Energy Butler GEN3 (battery)

The M-TEC Energy Butler GEN3 is a modular hybrid battery storage system with an integrated inverter, designed for residential and small commercial PV installations. This template communicates over Modbus TCP using RTU framing over the device's built-in network interface. It reads battery power (charge and discharge direction via sign) and state of charge, and exposes a writable battery mode register that lets your portal control operating behaviour. Connecting the Energy Butler GEN3 to ModbusCloud gives installers and asset managers live battery telemetry and remote mode control from a single dashboard.

Name	Address	Function	Type	Unit	Access
power Battery power, positive for discharge, negative for charge, watts.	30258	FC03	int32	W	R
soc Battery state of charge, 0 to 100 percent.	33000	FC03	uint16	%	R
batterymode Operating mode setpoint for the battery, written to control charge/discharge behaviour.	50000	FC16	uint16		W